Lithium separation member, lithium separation device, and method for manufacturing lithium separation member

Abstract

A lithium separation member 10 comprises: a lithium ion conductor layer 11 that selectively allows lithium ions to pass; and a support substrate 12 that supports the lithium ion conductor layer 11 and has a porous structure. For example, the lithium ion conductor layer 11 is a dense lithium ion conductor layer having a dense structure. Provided is a lithium separation member, etc., provided with an electrolyte membrane, the lithium separation member being resistant to cracking of the electrolyte membrane even if the electrolyte membrane is made thinner or increased in area.

Description

Lithium Separation Member, Lithium Separation Device, and Method for Manufacturing Lithium Separation Member

[0001] The present invention relates to a lithium separation member, a lithium separation device, and a method for manufacturing a lithium separation member. In particular, the present invention relates to a lithium separation member having a function of selectively permeating lithium ions.

[0002] In recent years, the demand for lithium has been expanding for applications such as lithium-ion batteries. Therefore, there is a need for a process that achieves both efficiency and environmental superiority in refining lithium, as well as for the resource circulation and recycling of lithium. As a method for refining lithium and recovering lithium resources, a technique for recovering lithium by electrodialysis using an electrolyte membrane has been proposed.

[0003] Patent Document 1 discloses a lithium-conductive sheet. This lithium-conductive sheet has a composition of Li ３Ｘ La ２／３－Ｘ TiO ３ (X is 0.05 or more and 0.3 or less), the area of the main surface is 20 cm ２ or more, the thickness is 10 μm or more and 1000 μm or less, the strain rate when viewed from the direction in which the main surface extends is 10 or less, and the average value of the measurement results of the lithium ion conductivity at 50 randomly selected locations is 3.0 × 10 －４ S / cm or more, and the standard deviation of the measurement results is 1.0 × 10 －４ S / cm or less.

[0004] Patent Document 2 discloses a metal ion recovery device. In this metal ion recovery device, a selective permeation membrane that selectively permeates Li is used, and a mesh-shaped positive electrode and negative electrode are respectively formed on both main surfaces of the flat selective permeation membrane. This structure is provided in a treatment tank, and the stock solution containing Li ions and the recovery solution, which is the destination where Li is recovered, are partitioned by this selective permeation membrane in the treatment tank. As the selective permeation membrane, lithium nitride (Li ３ N), Li １０ GeP ２ S １２ , (La ｘ , Li ｙ ) TiOｚ , Li １＋ｘ＋ｙ , Al ｘ (Ti, Ge) ２－ｘ , Si ｙ , P ３－ｙ , O １２ etc. can be used.

[0005] Japanese Patent Application Laid-Open No. 2023-54889, Japanese Patent Application Laid-Open No. 2015-34315

[0006] In order to increase the lithium recovery amount, reducing the resistance and increasing the area of the electrolyte membrane are effective. However, existing ceramic solid electrolyte membranes are prone to cracking, and there are limitations in thinning and increasing the area, and sufficient lithium processing capacity has not been obtained. As a conventional technique, the method of controlling the strain rate of the electrolyte membrane is insufficient to suppress cracks in the electrolyte membrane. Also, in the method of arranging a plurality of small electrolyte membranes in the in-plane direction to increase the processing capacity, it is necessary to bond / seal the electrolyte membranes to each other, and there are problems with the reliability of the sealing part. That is, cracks, peeling, and leakage due to deterioration of the adhesive are likely to occur at the sealing part. The present invention aims to provide a lithium separation member provided with an electrolyte membrane, etc., in which cracks are less likely to occur in the electrolyte membrane even when the electrolyte membrane is thinned or increased in area.

[0007] To solve the above problems, the present invention provides a lithium separation member including a lithium ion conductor layer that selectively transmits lithium ions and a support substrate that supports the lithium ion conductor layer and has a porous structure. The present invention also provides a lithium separation device including the above lithium separation member. Furthermore, the present invention provides a method for manufacturing a lithium separation member including a first sheet creation step of creating a first sheet that becomes the source of a lithium ion conductor dense layer including a lithium ion conductor that selectively transmits lithium ions and having a dense structure, a second sheet creation step of creating a second sheet that becomes the source of a support substrate that supports the lithium ion conductor dense layer and has a porous structure, and a firing step of firing the first sheet and the second sheet to form a lithium ion conductor dense layer and a support substrate.

[0008] A lithium separation member including an electrolyte membrane, and an object thereof is to provide a lithium separation member or the like in which cracks are less likely to occur in the electrolyte membrane even when the electrolyte membrane is thinned or enlarged in area.

[0009] It is a diagram showing a lithium separation device to which the present embodiment is applied. It is a diagram showing a first example of the lithium separation member of the present embodiment. It is a diagram showing the case where the lithium separation member having the structure of FIG. 2 is formed into a cylindrical shape. It is a diagram showing a second example of the lithium separation member of the present embodiment. It is a diagram showing a third example of the lithium separation member of the present embodiment. It is a diagram showing a fourth example of the lithium separation member of the present embodiment. It is a diagram showing the case where the lithium separation member of the present embodiment has a front-back symmetric structure. (A) to (b) are diagrams showing the lithium separation member of the present embodiment. It is a diagram showing an example of a method for manufacturing the lithium separation member of the present embodiment.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0011] <Explanation of Lithium Separation Device 1> FIG. 1 is a diagram showing a lithium separation device 1 to which the present embodiment is applied. The illustrated lithium separation device 1 is a device that separates and recovers lithium ions (Li ＋ ) from a lithium-containing solution. The lithium separation device 1 includes a lithium separation member 10, electrodes 20 and 30, and a solution tank 40. The lithium separation member 10 is a member that can selectively transmit lithium ions. The electrode 20 is a positive electrode, and the electrode 30 is a negative electrode. The solution tank 40 stores a lithium-containing solution and a recovered solution.

[0012] In this case, electrodes 20 and 30 are arranged on each of the two main surfaces of the lithium separation member 10. A lithium-containing solution is placed on the side of electrode 20, which becomes the positive electrode. The lithium-containing solution is created by refining lithium resources. Examples of lithium resources include seawater, roasted and leached liquid from discarded lithium-ion batteries (waste LIBs (Lithium Ion Batteries)), salt lake brine, and geothermal brine. On the side of electrode 30, which becomes the negative electrode, a recovered solution such as pure water or an aqueous lithium hydroxide solution is placed. When a DC voltage is applied between electrodes 20 and 30, lithium ions move from the positive electrode side 20 through the lithium separation member 10 to the negative electrode side 30. On the other hand, it is difficult for other ions to pass through the lithium separation member 10. In other words, the lithium separation member 10 can selectively allow lithium ions to pass through and separate them from other ions.

[0013] Then, carbon dioxide (CO2) is added to the recovered solution. ２ When you blow in lithium ions, lithium carbonate (Li ２ CO ３ It can be precipitated and recovered as lithium carbonate. Lithium carbonate is reused as a battery material.

[0014] <Explanation of the configuration of the lithium separation member 10> Next, the lithium separation member 10 will be described according to the first and second embodiments.

[0015] [First Embodiment] The first embodiment is characterized by a laminated structure of the lithium separation member 10. Figure 2 is a diagram showing a first example of the lithium separation member 10 of this embodiment. The illustrated lithium separation member 10 consists of a lithium ion conductor layer 11 and a support substrate 12. The lithium ion conductor layer 11 is an example of an electrolyte membrane and is a functional layer that selectively permeates lithium ions. The lithium ion conductor layer 11 contains a lithium ion conductor. The lithium ion conductor is, for example, a perovskite oxide, and more specifically, La ２／３-ｘ Li ３ｘ TiO ３This is a lithium ion conductive solid electrolyte ceramic lithium lanthanum titanate (LLTO) represented by . In this case, the lithium ion conductor is, for example, La ０．５７ Li ０．２９ TiO ３ It can be made into this composition.

[0016] However, this is not limited to the above, and a solid electrolyte material exhibiting lithium ion conductivity can be used for the lithium ion conductor layer 11. For example, Li １．５ Al ０．５ Ge １．５ (PO ４ ) ３ Polyanionic solid electrolytes having a Li-substituted NASICON-type structure, such as (LAGP), lithium lanthanum niobate: Li ５ La ３ Nb ２ O １２ Lithium lanthanum tantalate: Li ５ La ３ Ta ２ O １２ Lithium zirconate lanthanum: Li ７ La ３ Zr ２ O １２ (LLZO) and garnet-type solid electrolytes based on LLZO with various elements substituted, Li １＋ｘ Al ｘ Ti ２－ｘ (PO ４ ) ３ Lithium aluminum titanium phosphate (LATP), Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ - Lithium ion conductive glass ceramic (LICGC), represented by GeO, Li ２，９ PO ３．３ N ０．４６Lithium oxynitride phosphate (LASiPTTiGeO), LLTO nitride (LLTON), LLZO nitride (LLZON), LASiPTTiGeO nitride (LASiPTTiGeON), etc. may also be used.

[0017] The lithium-ion conductor layer 11 is a dense lithium-ion conductor layer with a dense structure. In other words, the lithium-ion conductor layer 11 has a low porosity, less than 10%. The dense structure enhances the selectivity of lithium ions. Furthermore, the thickness of the lithium-ion conductor layer 11 is preferably between 5 μm and 1000 μm. If the thickness of the lithium-ion conductor layer 11 is less than 5 μm, pores connecting the front and back surfaces are easily formed, making it difficult to selectively allow lithium ions to pass through. Also, if the thickness of the lithium-ion conductor layer 11 exceeds 1000 μm, the resistance increases, and the lithium separation performance tends to deteriorate. In addition, flexibility decreases, and the entire lithium separation member 10 becomes more prone to breakage when bent.

[0018] In this case, the lithium-ion conductor dense layer is the same as the lithium-ion conductor dense layer 111 described later, and it can also be said that the lithium-ion conductor layer 11 in Figure 2 is the lithium-ion conductor dense layer 111. Therefore, hereafter, the lithium-ion conductor layer 11 of the lithium separation member 10 in Figure 2 may be referred to as the lithium-ion conductor dense layer 111.

[0019] The support substrate 12 is a support that supports the lithium ion conductor layer 11. The support substrate 12 is, for example, yttria-stabilized zirconia (YSZ). In this case, zirconia (ZrO ２ A stabilizer containing yttrium oxide in an amount of 1.5 mol% to 10 mol% can be used. Preferably, the amount of yttrium oxide added is 2.5 mol% to 8 mol%, and more preferably 3.0 mol% to 5.5 mol%. Within this range, the strength of the support substrate 12 can be further increased, and damage to the lithium separation member 10 can be further suppressed.

[0020] However, this is not limited to the above, and the support base material 12 may be, for example, alumina (Al ２ O ３ ), Magnesia (MgO), Yttria (Y ２ O ３ ), mullite (Al ６ O １３ Si ２ ), spinel (MgAl ２ O ４ ), or a mixture of these may also be used.

[0021] Furthermore, the support substrate 12 has a porous structure. That is, the support substrate 12 has high porosity, with a porosity of 20% to 60%. The porosity is determined by polishing the cross section of the support substrate with a CP (cross-section polisher) and then obtaining an image magnified 1,000 to 20,000 times using an FE-SEM (field emission scanning electron microscope). Next, the cross section image is analyzed using the image analysis software HALCON manufactured by MVTec Corporation to highlight the porosity areas. Next, the total area of ​​the solid portion composed of the support substrate and the total area of ​​the porosity areas are determined from the analyzed cross section image. Next, the area occupancy rate of the porosity areas is calculated. This area occupancy rate of the porosity areas is calculated for five fields of view of the FE-SEM, and the arithmetic mean of these is taken as the porosity of the support substrate 12. If the porosity is less than 20%, it is difficult to form interconnected pores, and the resistance tends to increase. Also, if the porosity exceeds 60%, the strength of the lithium separation member 10 tends to be insufficient. Furthermore, the average pore diameter is preferably 0.1 μm or more and 50 μm or less. The average pore diameter is obtained by calculating the average equivalent circle diameter for each field of view in the five cross-sectional images after the analysis described above, and then taking the arithmetic mean of the average equivalent circle diameters for each field of view. The equivalent circle diameter is the diameter of a circle having the same area as the cross-sectional area of ​​the pores. By making the support substrate 12 porous, lithium can be separated when the raw solution or recovered solution permeates the support substrate 12 and comes into contact with the lithium ion conductor layer 11. The thickness of the support substrate 12 is preferably 0.5 mm or more and 10 mm or less. If the thickness of the support substrate 12 is less than 0.5 mm, the strength of the lithium separation member 10 tends to be insufficient. Also, if the thickness of the support substrate 12 exceeds 10 mm, the resistance increases and the lithium separation performance tends to decrease.

[0022] By providing the support substrate 12, the strength of the lithium separation member 10 is improved, and cracks in the lithium ion conductor layer 11 can be suppressed. Furthermore, since the strength can be ensured by the support substrate 12, it becomes easier to increase the area of ​​the lithium separation member 10. In addition, since the lithium ion conductor layer 11 can be formed as a thin film, it becomes possible to reduce resistance and improve the lithium recovery speed and amount.

[0023] The lithium separation member 10 of this embodiment can be rectangular in shape, for example, with dimensions of 50 mm or more and 300 mm or less. Alternatively, it may be disc-shaped, with dimensions of 50 mm or more and 300 mm or less. Conventionally, the size of the lithium separation member 10 was limited to approximately 50 mm or 50 mm in diameter, but this embodiment allows for a larger surface area than conventional designs. The lithium separation member 10 can also be cylindrical or rectangular. By making it cylindrical, the contact area with the raw liquid and the recovered liquid can be increased compared to using a plate-shaped lithium separation member, thereby improving the lithium recovery efficiency. Furthermore, the cylindrical shape allows for greater strength compared to the plate-shaped case.

[0024] Figure 3 shows a case where the lithium separation member 10 of the structure in Figure 2 is cylindrical. In the illustrated lithium separation member 10, the lithium ion conductor layer 11 is cylindrical on the outside, and the support base material 12 is cylindrical on the inside, so that the overall shape is also cylindrical. There is no particular upper limit to the opening diameter (maximum inner diameter) of the cylindrical lithium separation member 10, but for example it is 1000 mm or less, preferably 500 mm or less, and particularly preferably 150 mm or less. By using such a lithium separation member 10, the contact area between the raw solution or recovered solution and the lithium separation member 10 is increased, a sufficient amount of liquid can pass through the cylinder is secured, and the recovery efficiency of lithium contained in the raw solution can be improved. There is no particular limit to the length of the cylindrical lithium separation member 10, but for example it can be 10 mm or more, and preferably 100 mm or more. If the length of the selective permeable membrane is 10 mm or more, the contact area between the raw solution or recovered solution and the lithium separation member 10 can be increased, and the recovery efficiency of lithium contained in the raw solution can be improved. There is no particular upper limit to the length, but it is sufficient to set it to, for example, 2000 mm or less, and typically 1000 mm or less. The opening diameter and length of the cylindrical lithium separation member 10 should preferably be set to an appropriate combination considering the amount of liquid to be passed through and the contact efficiency between the lithium separation member 10 and the raw liquid or recovered liquid.

[0025] Figure 4 shows a second example of the lithium separation member 10 of this embodiment. The lithium separation member 10 shown includes a lithium ion conductor layer 11 consisting of a dense lithium ion conductor layer 111 and a porous lithium ion conductor layer 112. In other words, the lithium ion conductor layer 11 in Figure 4 has a laminated structure in which the dense lithium ion conductor layer 111 and the porous lithium ion conductor layer 112 are laminated together. The dense lithium ion conductor layer 111 is the same as the lithium ion conductor layer 11 in Figure 2 and has a dense structure.

[0026] The lithium-ion conductor porous layer 112 has the same composition as the lithium-ion conductor dense layer 111 and is a functional layer that selectively allows lithium ions to pass through. That is, the lithium-ion conductor porous layer 112 is, for example, a lithium-ion conductive solid electrolyte ceramic (LLTO).

[0027] The lithium-ion conductor porous layer 112 is disposed between the lithium-ion conductor dense layer 111 and the support substrate 12, and has a porous structure. That is, the lithium-ion conductor porous layer 112 has high porosity, with a porosity of 20% to 60%. Furthermore, the average pore diameter is preferably 0.1 μm to 50 μm. The porosity and average pore diameter of the lithium-ion conductor porous layer 112 are measured in the same way as the support substrate 12 described above. By making the lithium-ion conductor porous layer 112 porous, the surface area of ​​the lithium-ion conductor layer 11 is increased, and the resistance is reduced. Furthermore, it becomes possible to improve the lithium recovery rate and recovery amount. The thickness of the lithium-ion conductor porous layer 112 is preferably 5 μm to 500 μm. If the thickness of the lithium-ion conductor porous layer 112 is less than 5 μm, the effect of increasing the surface area is not easily achieved. Furthermore, if the thickness of the lithium-ion conductor porous layer 112 exceeds 500 μm, the effect of increased resistance in the thickness direction becomes significant, and the effect of improving lithium separation performance with respect to film thickness decreases. In addition, the lithium-ion conductor porous layer 112 may also be laminated on the upper side of the lithium-ion conductor dense layer 111. By providing the lithium-ion conductor porous layer 112 on both sides of the lithium-ion conductor dense layer 111, it becomes possible to further improve the lithium recovery rate and recovery amount.

[0028] Figure 5 shows a third example of the lithium separation member 10 of this embodiment. The lithium separation member 10 shown includes a lithium ion conductor layer 11 consisting of a dense lithium ion conductor layer 111 and a mixed layer 113. In other words, the lithium ion conductor layer 11 in Figure 5 has a laminated structure in which the dense lithium ion conductor layer 111 and the mixed layer 113 are stacked. The dense lithium ion conductor layer 111 is the same as the lithium ion conductor layer 11 in Figure 2 and has a dense structure.

[0029] The mixed layer 113 is a functional layer that adheres the lithium-ion conductor dense layer 111 to the support substrate 12. By providing the mixed layer 113, the adhesive strength between the lithium-ion conductor dense layer 111 and the support substrate 12 is improved and peeling can be suppressed. The mixed layer 113 has a composition in which the lithium-ion conductor and the support substrate material are mixed. That is, the mixed layer 113 is, for example, a layer in which lithium lanthanum titanate (LLTO) and yttria-stabilized zirconia (YSZ) are mixed. The mixing ratio of the lithium-ion conductor and the support substrate material can be 10 to 90% by volume. Preferably it is 20 to 80%, and more preferably 30 to 60%. The mixed layer 113 also has a porous structure similar to that of the support substrate 12. The porosity of the mixed layer 113 is preferably 20% to 60%. The average pore size is preferably 0.1 μm to 50 μm. The porosity and average pore size of the mixed layer 113 are measured in the same manner as the support substrate 12 described above. The thickness of the mixed layer 113 is preferably 5 μm or more and 200 μm or less. If the thickness of the mixed layer 113 is less than 5 μm, the effect of improving the bonding strength between the support substrate 12 and the lithium ion conductor layer 11 is small. If the thickness of the mixed layer 113 exceeds 200 μm, the effect of improving the bonding strength saturates, and resistance increases, making it easier for the lithium separation performance to deteriorate.

[0030] It can also be said that the lithium-ion conductor layer 11 in Figure 5 has a structure in which a portion of the lithium-ion conductor porous layer 112 is replaced by a supporting substrate material, compared to the lithium-ion conductor layer 11 in Figure 4.

[0031] Figure 6 shows a fourth example of the lithium separation member 10 of this embodiment. The lithium separation member 10 shown includes a lithium ion conductor layer 11 comprising a lithium ion conductor dense layer 111, a lithium ion conductor porous layer 112, and a mixed layer 113. In other words, the lithium ion conductor layer 11 in Figure 6 has a laminated structure in which the lithium ion conductor dense layer 111, the lithium ion conductor porous layer 112, and the mixed layer 113 are laminated together. The lithium ion conductor dense layer 111 is the same as the lithium ion conductor layer 11 in Figure 2 and has a dense structure. The lithium ion conductor porous layer 112 is the same as the lithium ion conductor porous layer 112 in Figure 4. The mixed layer 113 is the same as the mixed layer 113 in Figure 5.

[0032] The lithium separation member 10 in Figure 6 can provide all the effects of the lithium separation members 10 in Figures 2, 4-5. The lithium ion conductor dense layer 111 can also have a symmetrical structure. For example, the lithium ion conductor porous layer 112 may be present on both sides of the lithium ion conductor dense layer 111.

[0033] Figure 7 shows the lithium separation member 10 of Figure 6 with a front-to-back symmetrical structure. The lithium separation member 10 shown is laminated in the following order: support base material 12, mixed layer 113, lithium ion conductor porous layer 112, lithium ion conductor dense layer 111, lithium ion conductor porous layer 112, mixed layer 113, and support base material 12. In other words, the lithium ion conductor dense layer 111 is sandwiched between the lithium ion conductor porous layer 112, mixed layer 113, and support base material 12, which are laminated in the vertical direction in the figure, resulting in a front-to-back symmetrical structure. By adopting a front-to-back symmetrical structure, warping of the lithium separation member 10 can be suppressed and flattened, and damage can also be suppressed. Furthermore, the front-to-back symmetrical structure is not limited to the laminated structure of Figure 7; for example, the lithium separation member 10 shown in Figures 2 to 5 may also have a front-to-back symmetrical structure.

[0034] [Second Embodiment] In the second embodiment, the area of ​​the main surface of the support substrate 12 is larger than the area of ​​the main surface of the lithium ion conductor layer 11.

[0035] Figures 8(a) and 8(b) show the lithium separation member 10 of this embodiment. Figure 8(a) is a view of the lithium separation member 10 of this embodiment from the horizontal direction, and Figure 8(b) is a perspective view of the lithium separation member 10 of this embodiment. As shown in the figures, the area of ​​the main surface of the support base material 12 is larger than the area of ​​the main surface of the lithium ion conductor layer 11. The support base material 12 also has an edge portion 12a that surrounds the main surface of the lithium ion conductor layer 11. The edge portion 12a functions as a crack suppression portion when an external force is applied from the outer circumference of the lithium separation member 10. That is, even when an external force is applied from the outer circumference of the lithium separation member 10, the impact is absorbed by the edge portion 12a, so that damage is limited to the edge portion 12a and damage to the lithium ion conductor layer 11 can be suppressed. The width of the edge portion 12a is preferably, for example, 0.1 mm or more and 14% or less of the outer dimensions of the support base material 12. If the width of the edge portion 12a is less than 0.1 mm, it will not function well as a crack suppression portion. Also, if the width of the edge portion 12a exceeds 14% of the outer dimensions of the support base material 12, the area of ​​the main surface of the lithium ion conductor layer 11 will become too small, resulting in a large size of lithium separation device 1 relative to the lithium processing capacity and significant space loss.

[0036] <Explanation of the manufacturing method of the lithium separation member 10> The lithium separation member 10 may be manufactured by any method. For example, it can be manufactured by a combination of extrusion molding, mold casting, press molding, tape molding, printing, etc. Figure 9 is a diagram showing an example of the manufacturing method of the lithium separation member 10 of this embodiment. Here, the lithium separation member 10 is manufactured by producing corresponding green sheets by tape molding, laminating these green sheets, and then pressing and firing them.

[0037] (Preparation of lithium-ion conductor dense layer 111 green sheet) The lithium-ion conductor dense layer 111 green sheet may be manufactured by any method. For example, it can be manufactured as follows. First, a lithium-ion conductor dense layer slurry is prepared by mixing LLTO powder, a dispersant, a solvent, a plasticizer, and a binder. The prepared slurry is then formed into a sheet on a PET film using the doctor blade method to form a green sheet that will become the lithium-ion conductor dense layer 111. At this time, the thickness of the lithium-ion conductor dense layer 111 green sheet can be adjusted by adjusting the coating thickness.

[0038] (Preparation of the support substrate 12 green sheet) The support substrate 12 can be manufactured by any method, such as extrusion molding, tape molding, mold casting, or press molding. For example, in the case of tape molding, it can be manufactured as follows. First, a zirconia slurry is prepared by mixing zirconia powder, a dispersant, a solvent, a plasticizer, a binder, and a pore-forming agent. The prepared slurry is then formed into a sheet on a PET film using the doctor blade method to form a green sheet that will become the support substrate 12. At this time, the thickness of the support substrate 12 green sheet can be adjusted by adjusting the coating thickness. In addition, the porosity of the support substrate 12 can be controlled by adjusting the amount of pore-forming agent added, and the pore size of the support substrate 12 can be controlled by adjusting the particle size of the pore-forming agent.

[0039] (Preparation of Lithium Ion Conductor Porous Layer 112 Green Sheet) The lithium ion conductor porous layer 112 green sheet may be manufactured by any method, but for example, it can be manufactured as follows. First, a lithium ion conductor porous layer slurry is prepared by mixing LLTO powder, a dispersant, a solvent, a plasticizer, a binder, and a pore-forming material. The prepared slurry can be formed into a sheet on a PET film using the doctor blade method to form the lithium ion conductor porous layer 112 green sheet. At this time, the thickness of the lithium ion conductor porous layer 112 green sheet can be adjusted by adjusting the coating thickness. In addition, the porosity of the support substrate 12 can be controlled by adjusting the amount of pore-forming material added, and the pore diameter of the support substrate 12 can be controlled by adjusting the particle size of the pore-forming material.

[0040] (Preparation of Mixed Layer 113 Green Sheet) The mixed layer 113 green sheet may be manufactured by any method, but for example, it can be manufactured as follows. First, a mixed layer slurry is prepared by mixing LLTO powder, zirconia powder, a dispersant, a solvent, a plasticizer, a binder, and a pore-forming agent. The prepared slurry can be formed into a sheet on a PET film using the doctor blade method to form the mixed layer 113 green sheet. At this time, the thickness of the mixed layer 113 green sheet can be adjusted by adjusting the coating thickness. In addition, the porosity of the support substrate 12 can be controlled by adjusting the amount of pore-forming agent added, and the pore diameter of the support substrate 12 can be controlled by adjusting the particle size of the pore-forming agent.

[0041] (Lamination and firing) Each green sheet is cut, and a predetermined number of sheets are laminated and pressed together according to the thickness of each layer (cutting / lamination). Lamination can be carried out by known methods and is not particularly limited, but a CIP (cold isostatic pressing) molding machine or a uniaxial press molding machine can be used. The preferred pressing pressure is 10 to 5000 kgf / cm ２ More preferably, 50 to 3000 kgf / cm² ２The structure shown in Figures 2, 4 to 6 can be created by varying the type of green sheet used for layering. Furthermore, the thickness of the lithium-ion conductor dense layer 111, the lithium-ion conductor porous layer 112, the mixed layer 113, and the support substrate 12 can be controlled by adjusting the thickness and number of layers of each layer of green sheet.

[0042] Then, the laminated green sheets are cut to a predetermined shape and size and fired (1150-1500°C, 1-10 hours). That is, the green sheets that will become the lithium ion conductor dense layer 111 and the green sheets that will become the support substrate 12 are fired together, and they become the lithium ion conductor dense layer 111 and the support substrate 12, respectively. In this way, a lithium separation member 10 can be manufactured in which the lithium ion conductor dense layer 111 and the support substrate 12 are laminated, for example, as shown in Figure 2. Furthermore, in the above example, the lithium separation member 10 was manufactured by laminating the green sheets of the lithium ion conductor dense layer 111 and the support substrate 12 and firing them together, but the lithium ion conductor dense layer 111 and the support substrate 12 may also be manufactured by firing them sequentially or separately. Specifically, the green sheets that will become the lithium ion conductor dense layer 111 and the green sheets that will become the support substrate 12 are laminated separately, and the green sheet that will become the support substrate 12 is fired once to manufacture the support substrate 12. Then, a green sheet that will become the lithium-ion conductor dense layer 111 may be laminated onto the manufactured support substrate 12 and fired. Alternatively, the green sheet that will become the lithium-ion conductor dense layer 111 may be fired separately, and the manufactured lithium-ion conductor dense layer 111 and the support substrate 12 may be joined together.

[0043] The manufacturing method for the lithium separation member 10 shown in Figure 9 can be understood as a method for manufacturing the lithium separation member 10 that includes: a first sheet creation step of creating a first sheet (in this case, a green sheet that will become the lithium ion conductor dense layer 111) which will be the basis of a lithium ion conductor dense layer 111 having a dense structure and containing a lithium ion conductor that selectively allows lithium ions to pass through; a second sheet creation step of creating a second sheet (in this case, a green sheet that will become the basis of the support base material 12) which will be the basis of a support base material 12 having a porous structure that supports the lithium ion conductor dense layer 111; and a firing step of firing the first sheet and the second sheet to form the lithium ion conductor dense layer 111 and the support base material 12.

[0044] <Explanation of Effects> In the first embodiment, by laminating the lithium ion conductor layer 11, which is an electrolyte membrane, with the support substrate 12, it is possible to provide a lithium separation member 10 that is less prone to cracking in the lithium ion conductor layer 11 even when the lithium ion conductor layer 11 is made thinner or has a larger surface area. Furthermore, as shown in Figure 4, by making the lithium ion conductor layer 11 a laminated structure of a lithium ion conductor dense layer 111 and a lithium ion conductor porous layer 112, the surface area of ​​the lithium ion conductor layer 11 is increased, and the resistance becomes smaller. Furthermore, it becomes possible to improve the lithium recovery rate and recovery amount. Moreover, as shown in Figure 5, when the lithium ion conductor layer 11 is a laminated structure of a lithium ion conductor dense layer 111 and a mixed layer 113, the adhesive strength between the lithium ion conductor dense layer 111 and the support substrate 12 is improved, and peeling can be suppressed. Furthermore, as shown in Figure 6, when the lithium-ion conductor layer 11 has a laminated structure consisting of a dense lithium-ion conductor layer 111, a porous lithium-ion conductor layer 112, and a mixed layer 113, all of the above effects can be achieved.

[0045] Furthermore, as in the second embodiment, if the area of ​​the main surface of the support substrate 12 is larger than the area of ​​the main surface of the lithium ion conductor layer 11, even when an external force is applied from the outer circumference of the lithium separation member 10, the impact can be absorbed at the edge 12a, thereby limiting the damage to the edge 12a and suppressing damage to the lithium ion conductor layer 11.

[0046] The following describes embodiments of the present invention. In this example, lithium-ion conductive solid electrolyte ceramics (LLTO) were used as the lithium-ion conductor.

[0047] [Examples 1-14] In Examples 1-14, the lithium separation member 10 shown in Figure 2 was fabricated. In Examples 1-14, the support substrate 12 was made of 3.0 mol% yttria-stabilized zirconia (3YSZ).

[0048] (Preparation of the green sheet that will become the lithium-ion conductor dense layer 111) First, an LLTO slurry was prepared by mixing LLTO powder, a dispersant, a solvent, a plasticizer, and a binder. The prepared LLTO slurry was formed into a sheet on a PET film using the doctor blade method to form a green sheet that will become the lithium-ion conductor dense layer 111. The thickness of this green sheet was set to 10 μm after firing.

[0049] (Preparation of the green sheet that will become the support substrate 12) First, a zirconia slurry was prepared by mixing 3YSZ powder, a dispersant, a solvent, a plasticizer, a binder, and polymethyl methacrylate beads as a pore-forming material. The prepared zirconia slurry was formed into a sheet on a PET film using the doctor blade method to form the green sheet that will become the support substrate 12. The thickness of this green sheet was set to 200 μm after firing. At this time, the porosity and average pore diameter were adjusted for each sample by adjusting the particle size and amount of the pore-forming material added, as shown in Table 1.

[0050] (Lamination, compression, and firing) One green sheet to form the lithium-ion conductor dense layer 111 and ten green sheets to form the support substrate 12 are stacked, and the resulting laminate is subjected to CIP (cold isostatic pressing) at 200 kgf / cm². ２ The green sheets were pressed together to bond them to each other. The resulting laminate was then cut to a size of 50 mm x 50 mm after firing to obtain a rectangular laminate. The obtained rectangular laminate was fired at 1300°C for 2 hours in air to obtain the lithium separation member 10 shown in Figure 2.

[0051] [Examples 15-18] In Examples 15-18, the support substrate 12 was made of a composition other than 3.0 mol% yttria-stabilized zirconia (3YSZ). Specifically, in Examples 15-18, as shown in Table 1, the support substrate 12 was made of 4.0 mol% yttria-stabilized zirconia (4YSZ), 5.0 mol% yttria-stabilized zirconia (5YSZ), 6.0 mol% yttria-stabilized zirconia (6YSZ), and 8.0 mol% yttria-stabilized zirconia (8YSZ), respectively.

[0052] [Examples 19-22] In Examples 19-22, the support substrate 12 was made of 8.0 mol% yttria-stabilized zirconia (8YSZ) with a thickness of 5 mm. The average pore size was then varied. Specifically, in Examples 19-22, as shown in Table 1, the thickness of the support substrate 12 was 10 μm, 20 μm, 50 μm, and 60 μm, respectively.

[0053] [Examples 23-28] In Examples 23-28, the porosity of the support substrate 12 was varied. Specifically, in Examples 23-25, as shown in Table 1, the thickness of the support substrate 12 was 2 mm, and the porosity was set to 50%, 60%, and 70%, respectively. In Examples 26-28, as shown in Table 1, the thickness of the support substrate 12 was 5 mm, and the porosity was set to 50%, 60%, and 70%, respectively.

[0054] [Examples 29-30] In Examples 29-30, lithium isolation members 10 were prepared to evaluate the film resistance described later. In Examples 29-30, as shown in Table 2, the thickness of the support substrate 12 was set to 2 mm, and the porosity was set to 20% and 30%, respectively.

[0055] [Comparative Example 1] In Comparative Example 1, a green sheet to be the basis of the lithium ion conductor dense layer 111 was prepared in the same manner as in Example 1, so that its thickness after firing was 100 μm. Five of these green sheets were then stacked and fired in the same manner as in Example 1 to create a lithium separation member consisting solely of the lithium ion conductor dense layer 111.

[0056]

[0057]

[0058] (Strength Evaluation) A puncture test was performed on the obtained lithium separation member 10 to evaluate the load at which it broke. For Examples 1 to 28, the lithium ion conductor dense layer 111 was placed on the lower side, and a load was applied from the support base material 12 side using a pin. Using the breaking load of Comparative Example 1 without a support base material as a baseline, those with improved strength compared to the comparative example were evaluated as ○, and those with strength 10 times or more than that of Comparative Example 1 were evaluated as ◎.

[0059] (Results of Strength Evaluation) As shown in Table 1, Examples 1 to 28, which were provided with the support substrate 12, were able to improve the fracture load even when the lithium ion conductive layer was made thin, compared to Comparative Example 1, which did not have the support substrate 12. Furthermore, comparing Examples 1 to 14 and 19 to 22, Examples 1 to 10 and 19 to 21, which had an average pore diameter of 50 μm or less, were able to improve the fracture load by more than 10 times. When the composition of the support substrate 12 was changed, the fracture load was improved in all cases. Comparing Examples 2 and 15 to 18, in particular, Examples 2 (3YSZ) and 15 (4YSZ) were able to improve the fracture load by more than 10 times. When the porosity of the support substrate 12 was changed, comparing Examples 23 to 28, in particular, Examples 23, 24, 26, and 27, which had a porosity of 60% or less, were able to improve the fracture load by more than 10 times.

[0060] (Resistance Evaluation) The film resistance of the obtained lithium isolation member was measured by the AC impedance method. At this time, Pt-plated titanium plates were used as electrodes 20 and 30. Electrode 20 was inserted into the tank on the raw solution side, and electrode 30 was inserted into the tank on the recovered solution side. Both the raw solution and the recovered solution were 0.1 mol lithium hydroxide aqueous solution. Measurements were performed in the frequency range of 1 MHz to 0.1 Hz, and the applied voltage was 3 V. From the obtained impedance spectrum, the resistance component was calculated from equivalent circuit analysis and the conductivity of the solution, and the sum of the resistances of the lithium ion conductor dense layer 111 and the support substrate 12 was defined as the film resistance. In Comparative Example 1, since there was no support substrate 12, the resistance of the lithium ion conductor dense layer 111 was defined as the film resistance. The evaluation results of the film resistance are shown in Table 2. It was confirmed that the film resistance of both Examples 29 and 30 was lower than that of Comparative Example 1.

[0061] Although this embodiment has been described above, the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear from the claims that various modifications or improvements made to the above embodiment are also included in the technical scope of the present invention.

[0062] 1...Lithium separation device, 10...Lithium separation member, 11...Lithium ion conductor layer, 12...Support substrate, 12a...Edge, 111...Lithium ion conductor dense layer, 112...Lithium ion conductor porous layer, 113...Mixed layer

Claims

1. A lithium separation member comprising: a lithium ion conductor layer that selectively permeates lithium ions; and a support substrate having a porous structure that supports the lithium ion conductor layer.

2. The lithium separation member according to claim 1, wherein the lithium ion conductor layer is a dense lithium ion conductor layer having a dense structure.

3. The lithium separation member according to claim 2, wherein the lithium ion conductor layer includes, in addition to the lithium ion conductor dense layer, a lithium ion conductor porous layer disposed between the lithium ion conductor dense layer and the support substrate and having a porous structure.

4. The lithium separation member according to claim 2, wherein the lithium ion conductor layer comprises, in addition to the lithium ion conductor dense layer, a mixed layer having a porous structure disposed between the lithium ion conductor dense layer and the support substrate, bonding the lithium ion conductor dense layer and the support substrate.

5. The lithium separation member according to claim 2, wherein the lithium ion conductor layer comprises, in addition to the lithium ion conductor dense layer, a lithium ion conductor porous layer having a porous structure disposed between the lithium ion conductor dense layer and the support substrate, and a mixed layer having a porous structure that adheres the lithium ion conductor porous layer and the support substrate.

6. The lithium separation member according to claim 2, wherein the lithium ion conductor dense layer has a thickness of 5 μm or more and 1000 μm or less.

7. The lithium separation member according to claim 1, wherein the support base material is yttria-stabilized zirconia.

8. The lithium separation member according to claim 7, wherein the support substrate has an average pore diameter of 50 μm or less.

9. The lithium separation member according to claim 7, wherein the support substrate has a porosity of 20% or more and 60% or less.

10. The lithium separation member according to claim 1, wherein the area of ​​the main surface of the support substrate is greater than the area of ​​the main surface of the lithium ion conductor layer.

11. The lithium separation member according to claim 10, wherein the support substrate has an edge portion surrounding the main surface of the lithium ion conductor layer.

12. The lithium separation member according to claim 1, wherein the shape is cylindrical.

13. A lithium separation apparatus comprising a lithium separation member according to any one of claims 1 to 12.

14. A method for manufacturing a lithium separation member, comprising: a first sheet preparation step of creating a first sheet that will serve as the basis for a dense lithium ion conductor layer having a dense structure and containing a lithium ion conductor that selectively permeates lithium ions; a second sheet preparation step of creating a second sheet that will serve as the basis for a support substrate having a porous structure that supports the dense lithium ion conductor layer; and a firing step of firing the first sheet and the second sheet to form the dense lithium ion conductor layer and the support substrate, respectively.

Images