Method for producing solid electrolyte

Abstract

To provide a manufacturing method of a solid electrolyte capable of reducing deterioration of yield.SOLUTION: The method for producing a solid electrolyte includes a step of firing a material of the solid electrolyte in a sagger, and the sagger includes a container including a bottom and a wall provided around the bottom, and a plate disposed on the bottom. The solid state reaction at the firing temperature when the material is in contact with the plate and the wall is less likely to occur between the plate and the material than between the wall and the material, and the flexural strength of the base at the firing temperature is greater than the flexural strength of the plate at the firing temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid electrolyte. [Background technology]

[0002] The manufacturing method of a solid electrolyte includes a step of firing the material of the solid electrolyte in a sagger. Patent Document 1 discloses a prior art technique in which the material is fired in a sagger (plate) made of magnesia. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-40767 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, the reaction between the sagger and the material at the firing temperature or the thermal strain generated in the sagger can cause the sagger to crack during firing, causing the material to fall from the sagger into the furnace, resulting in a decrease in the yield of the solid electrolyte.

[0005] The present invention has been made to solve this problem, and has as its object to provide a method for producing a solid electrolyte that can reduce the deterioration of the yield. [Means for solving the problem]

[0006] A first aspect of the present invention to achieve this object includes a step of sintering a solid electrolyte material in a sagger, the sagger comprising a container including a bottom and a wall surrounding the bottom, and a plate disposed on the bottom, wherein a solid-state reaction between the material and the plate and the wall at the sintering temperature is less likely to occur than a reaction between the plate and the material, and the flexural strength of the bottom at the sintering temperature is greater than the flexural strength of the plate at the sintering temperature.

[0007] In the second embodiment, in the first embodiment, the container is mainly made of alumina and the plate is mainly made of magnesia.

[0008] In a third aspect, in the first or second aspect, the solid electrolyte is an oxide-based solid electrolyte.

[0009] In a fourth aspect, in any one of the first to third aspects, the solid electrolyte contains lithium.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the solid electrolyte has a garnet-type crystal structure containing Li, La, Zr, and O.

[0011] In a sixth embodiment, in the fifth embodiment, the solid electrolyte contains Mg and Sr. [Effects of the Invention]

[0012] According to the present invention, the solid-state reaction at the firing temperature is less likely to occur between the plate and the material than between the wall and the material, thereby reducing contamination of the material by the sagger. The bending strength of the bottom at the firing temperature is greater than the bending strength of the plate at the firing temperature, so even if the plate cracks during firing, the bottom is less likely to crack. The material can be prevented from falling from the sagger into the furnace, reducing deterioration in the yield of the solid electrolyte. [Brief explanation of the drawings]

[0013] [Figure 1] 1(a) is a cross-sectional view of a sagger in one embodiment, and FIG. 1(b) is a cross-sectional view of the sagger after firing the material. [Figure 2] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1(a) is a cross-sectional view of a sagger 11 in one embodiment. In the sagger 11, a solid electrolyte material 10 is fired.

[0015] The solid electrolyte can be any crystalline or amorphous material such as sulfide, hydroxide, or oxide. Sulfide-based solid electrolytes include crystalline thiolithium type, Li 10 GeP2S 12 type, argyrodite type, Li7P3S 11 Examples of hydride-based solid electrolytes include solid solutions of LiBH4 with lithium halide compounds (LiI, LiBr, LiCl) and lithium amide (LiNH2).

[0016] Examples of oxide-based solid electrolytes include NASICON-based materials, LISICON-based materials, and oxides having a perovskite structure or a garnet structure.

[0017] NASICON-based materials are of the general formula A x It is a material represented by M2(TO4)3. Examples of A are Na and Li, examples of M are Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and examples of T are P, Si, and As. For example, Na3V2(PO4)3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Ge x Ti 2-x (PO4)3. LISICON-based materials include Li 4-2x Zn x GeO4 (0≦x≦1). Oxides with a perovskite structure include Li x La (1-x) / 3 NbO3, La 2 / 3-X Li 3X The crystal structure of garnet-type oxides is represented by the general formula C3A2B3O 12 It is expressed as:

[0018] FIG. 2 is a schematic diagram showing a garnet-type crystal structure. In the garnet-type crystal structure, Sc in the C-site is dodecahedrally coordinated with an oxygen atom Oa, Sa in the A-site is octahedrally coordinated with an oxygen atom Oa, and Sb in the B-site is tetrahedrally coordinated with an oxygen atom Oa. In the garnet-type crystal structure, Li can exist in a vacancy V, which is a position octahedrally coordinated with an oxygen atom Oa. The vacancy V is, for example, a position sandwiched between the B-site Sb1 and the B-site Sb2. The Li present in the vacancy V is octahedrally coordinated with an oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 that forms the B-site Sb1 and the tetrahedral face Fb2 that forms the B-site Sb2.

[0019] For example, Li7La3Zr2O 12 In the garnet-type solid electrolyte having the above composition, La occupies the C-site Sc, Zr occupies the A-site Sa, and Li occupies the B-site Sb and the vacant V. The garnet-type solid electrolyte is listed in X-ray diffraction file No. 422259 (Li7La3Zr2O) of the CSD (Cambridge Structural Database). 12 ) has a similar XRD pattern.

[0020] Garnet-type solid electrolytes are substituted with various elements. 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. The amount of lithium changes as a result of element substitution, and the arrangement, occupancy rate, and occupied sites of lithium ions within the crystal structure change, which in turn changes the ionic conductivity. The diffraction angle and intensity ratio may differ compared to No. 422259 due to element substitution.

[0021] Li7La3Zr2O 12 In the case of the tantalum oxide, some of the constituent elements may be substituted with other elements, or a small amount of other elements may be added without substituting the constituent elements. Examples of the 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).

[0022] 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 Ga 0.23 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<o000073>Zr2O 12 are examples.

[0023] It should be noted that there is a small error in the original text where "<o000073>" should probably be " 0.05 ", and this has been corrected in the translation.The garnet-type solid electrolyte preferably contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba) in which the molar ratio of each element satisfies all of the following (1) to (3), or contains both Mg and element A in which the molar ratio of each element satisfies all of the following (4) to (6). Element A is preferably Sr, as it increases 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

[0024] Returning to FIG. 1(a), the material 10 may be, for example, a powder or a compact formed by applying pressure to the powder or agglomerating the powder. Examples of the powder include a mixture of various metal salts such as oxides, hydroxides, and carbonates containing the metal elements that make up the solid electrolyte, and powders prepared by a solid-phase method, a liquid-phase method, a gas-phase method, or the like. The means for mixing the various metal salts may be wet mixing or dry mixing, without any restrictions.

[0025] The ratio of metal elements in material 10 is set to a value that matches or approximates the stoichiometric composition to the extent that the desired solid electrolyte is obtained. When material 10 contains a specific metal element that is easily lost during firing, such as lithium, the specific metal element may be contained in an excess amount relative to the stoichiometric composition.

[0026] Firing material 10 is one of the steps in producing a solid electrolyte. Material 10 is fired in a sagger 11 (a fireproof container). Sagger 11 includes a container 12 and a plate 15. Both container 12 and plate 15 are fireproof. Container 12 includes a bottom 13 and a wall 14 surrounding bottom 13. Examples of the shape of bottom 13 include polygons such as triangles and squares, and circles such as circles and ellipses. Bottom 13 may have one or more holes penetrating it, as long as the mechanical strength of bottom 13 can be ensured at the firing temperature. There are no particular limitations on the shape or size of the holes, as long as the mechanical strength of bottom 13 can be ensured.

[0027] The wall 14 is provided around the entire periphery of the bottom 13 and surrounds the entire bottom 13. The wall 14 may be perpendicular to the bottom 13, or the wall 14 may extend outside the bottom 13 so that the width of the wall 14 gradually increases with increasing distance from the bottom 13. The container 12 may be an integrally molded product in which the bottom 13 and the wall 14 are integrated, or the bottom 13 and the wall 14 may be bonded together.

[0028] Plate 15 is placed on the bottom 13 of container 12. The shape of plate 15 is approximately the same as the shape of bottom 13 to reduce the distance (gap) between the outer periphery of plate 15 and wall 14. The reason for reducing the gap is to reduce the amount of material 10 that gets between the edge of plate 15 and wall 14 and comes into contact with bottom 13. Note that if the linear expansion coefficient of plate 15 between room temperature and the firing temperature is greater than the linear expansion coefficient of bottom 13 between room temperature and the firing temperature, the dimensions of plate 15 are set so that a small gap is formed between plate 15 and wall 14 at room temperature. This is to prevent wall 14 from being damaged by plate 15, which expands relatively due to the heat during firing.

[0029] Examples of materials for the container 12 include alumina, cordierite, mullite, and silica. The materials for the bottom 13 and the walls 14 of the container 12 may be different or the same. It is preferable that both the bottom 13 and the walls 14 are made of a material containing alumina as the main component, since this ensures mechanical strength at firing temperatures. "Mainly containing alumina" means that 50 wt% or more of the material for the bottom 13 or the walls 14 is alumina.

[0030] Examples of the material of plate 15 include magnesia and zirconia. Plate 15 made of a material containing magnesia as its main component is preferable because it can reduce the solid-phase reaction between plate 15 and material 10 at the firing temperature. "Magnetic oxide as the main component" means that 50 wt% or more of the material of plate 15 is magnesia.

[0031] Material 10 is generally fired two or more times. The main purpose of the first firing (hereinafter referred to as "first firing") is to thermally decompose material 10. The first firing facilitates the formation of a solid electrolyte structure in the second firing (hereinafter referred to as "second firing"). Material 10 after first firing may have a solid electrolyte structure. Performing first firing and second firing is an example, and the number of firings is not limited to two. The number of firings may be more or less than two.

[0032] In the case of a garnet-type solid electrolyte, the temperature of the primary firing is, for example, 850°C or higher and 1150°C or lower. The primary firing may include a step of firing at a lower temperature within this temperature range and a step of firing at a higher temperature. Before the next firing step, the material 10 after each step may be crushed and mixed. In this case, it is preferable to crush the material 10 in a dry manner. The time of the primary firing is, for example, 10 hours or higher and 15 hours or lower at the set maximum temperature.

[0033] The material 10 in the sagger 11 is subjected to the first firing in a state where part of the material 10 is in contact with the plate 15 and part of the material 10 is in contact with the wall 14. The materials of the plate 15 and the wall 14 are selected so that a solid-phase reaction between the plate 15 and the material 10 during the first firing is less likely to occur than a solid-phase reaction between the wall 14 and the material 10.

[0034] The force with which the portion of material 10 in contact with plate 15 is pressed against plate 15 due to the weight of material 10 is greater than the force with which the portion of material 10 in contact with wall 14 is pressed against wall 14 due to the weight of material 10. The greater this force, the more likely material 10 will stick during firing, but a solid-state reaction between plate 15 and material 10 is less likely to occur than a solid-state reaction between wall 14 and material 10, so contamination of material 10 due to diffusion of material from plate 15 and sticking of material 10 to plate 15 can be reduced. Since there is no need to dispose of the portion of material 10 in contact with plate 15 or the stuck portion, loss of material 10 due to disposal can be reduced.

[0035] On the other hand, a solid-state reaction between wall 14 and material 10 is more likely to occur than a solid-state reaction between plate 15 and material 10. However, the force with which the portion of material 10 in contact with wall 14 is pressed against wall 14 due to the weight of material 10 is smaller than the force with which the portion of material 10 in contact with plate 15 is pressed against plate 15 due to the weight of material 10, so contamination of material 10 due to diffusion of material from wall 14 and adhesion of material 10 to wall 14 can be reduced. Since it is not necessary to dispose of the portion of material 10 in contact with wall 14 or the adhered portion, loss of material 10 due to disposal can be reduced.

[0036] A comparison of the likelihood of a reaction occurring between plate 15 and material 10 and the likelihood of a reaction occurring between wall 14 and material 10 can be predicted, for example, by inputting the chemical formulas of the solid electrolyte, wall 14, and plate 15 materials into Interface Reaction in the MaterialsProject (https: / / next-gen.materialsproject.org / ) database, which uses first-principles calculations. Alternatively, a sample can be actually prepared by placing material 10 on a test piece made from the material of plate 15 and firing it, and a sample can be prepared by placing material 10 on a test piece made from the material of wall 14 and firing it, and analyzing the amount of material 10 diffused into each sample and the amount of material 10 adhered to each sample. It can be said that a sample with a larger amount of material 10 diffused or adhered is more likely to undergo a reaction.

[0037] The materials and thicknesses of the plate 15 and the bottom 13 are set so that the bending strength of the bottom 13 at the firing temperature is greater than the bending strength of the plate 15 at the firing temperature. This makes it difficult for the bottom 13 to crack even if the plate 15 cracks during firing. If the plate 15 cracks, the wall 14 provided around the bottom 13 limits the movement of the plate 15 to prevent the crack from spreading, so the material 10 remains on the plate 15. Even if the material 10 falls from the plate 15, the material 10 remains on the bottom 13. Since the material 10 can be prevented from falling from the sagger 11 into the furnace, the loss of the material 10 due to falling from the sagger 11 can be reduced. Therefore, the deterioration of the solid electrolyte yield (the ratio of the amount of solid electrolyte to the amount of raw material used) can be reduced.

[0038] FIG. 1(b) is a cross-sectional view of a sagger 11 after the first firing of material 10. During the first firing, thermal decomposition of material 10 occurs and material transfer occurs between the particles of material 10, causing material 10 to shrink during the first firing. After the first firing, a gap is formed between material 10 and wall 14, and material 10 is no longer in contact with wall 14. If the second firing is performed while maintaining this state, the reaction between material 10 and wall 14 during the second firing can be reduced, thereby reducing contamination of material 10 due to diffusion of the material from wall 14.

[0039] The main purpose of the secondary firing is to synthesize a solid electrolyte. In the case of a garnet-type solid electrolyte, the secondary firing temperature is, for example, 1100°C or higher and 1250°C or lower. The secondary firing time is, for example, 10 hours or higher and 20 hours or lower at the set maximum temperature. To prevent loss of some elements due to heating, the material 10 may be covered with a lid 16 during the secondary firing. An example of the material for the lid 16 is magnesia.

[0040] The material 10 after the second firing may be removed from the sagger 11, pressure may be applied to the removed material 10 to form a compact, the compact may be placed on a plate 15, and the lid 16 may be placed on top of the compact and fired. The firing temperature and time at this time are the same as those for the second firing.

[0041] Alternatively, the material 10 after the primary firing may be removed from the sagger 11, pressure may be applied to the removed material 10 to produce a molded body, and the molded body may be placed on a plate 15 for secondary firing. In this case, the secondary firing may be performed with a lid 16 on the molded body, or the molded body may be covered with the material 10 after the primary firing and the secondary firing may be performed.

[0042] The produced solid electrolyte can be used as a material for electricity 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 that combine an electric double layer capacitor with a solid electrolyte.

[0043] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention. [Explanation of symbols]

[0044] 10 Solid electrolyte materials 11 Sack Bowl 12 containers 13 bottom 14 Wall 15 boards

Claims

1. 1. A method for producing a solid electrolyte, comprising: firing a material for the solid electrolyte in a sagger; The sagger comprises a container including a bottom and a wall surrounding the bottom; a plate disposed on the bottom, When the material contacts the plate and the wall, a solid-state reaction at the firing temperature occurs less frequently between the plate and the material than between the wall and the material; A method for manufacturing a solid electrolyte, wherein the bending strength of the bottom at the firing temperature is greater than the bending strength of the plate at the firing temperature.

2. 2. The method for producing a solid electrolyte according to claim 1, wherein the container is made mainly of alumina and the plate is made mainly of magnesia.

3. 3. The method for producing a solid electrolyte according to claim 1, wherein the solid electrolyte is an oxide-based solid electrolyte.

4. The method for producing a solid electrolyte according to claim 1 or 2, wherein the solid electrolyte contains lithium.

5. 3. The method for producing a solid electrolyte according to claim 1, wherein the solid electrolyte has a garnet-type crystal structure containing Li, La, Zr, and O.

6. 6. The method for producing a solid electrolyte according to claim 5, wherein the solid electrolyte contains Mg and Sr.

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