Lithium separation member, lithium separation device, and method of producing lithium separation member

Abstract

A lithium separation member 10 comprises: a lithium-ion conductor layer 11 that selectively allows lithium ions to pass therethrough; a support substrate 13 that supports the lithium-ion conductor layer 11 and contains tetragonal zirconia; and an intermediate 12 that is provided between the lithium-ion conductor layer 11 and the support substrate 13 has a higher monoclinic zirconia content than the support substrate 13. Provided thereby are a lithium separation member provided with an electrolyte membrane, wherein problems such as cracking occurring in the electrolyte membrane are less likely to occur even if tetragonal zirconia is contained in the support substrate.

Description

Lithium separation member, lithium separation apparatus, and method for producing lithium separation member

[0001] The present invention relates to a lithium separation member, a lithium separation apparatus, and a method for producing 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, demand for lithium for applications such as lithium ion storage batteries has been expanding. Therefore, there is a need for processes that achieve both improved efficiency and environmental advantages when refining lithium, as well as resource recycling and recycling of lithium. As methods for refining lithium and recovering lithium resources, techniques for recovering lithium by electrodialysis using an electrolyte membrane have 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 (wherein 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 distortion rate when viewed from the direction in which the main surface extends is 10 or less, and the average value of lithium ion conductivity measurement results 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 apparatus. In this metal ion recovery apparatus, a selectively permeable membrane that selectively permeates Li is used, and a mesh-shaped positive electrode and a mesh-shaped negative electrode are respectively formed on both main surfaces of the plate-shaped selectively permeable membrane. This structure is provided in a treatment tank, and the stock solution containing Li ions and the recovery liquid from which Li is recovered are partitioned by the selectively permeable membrane in the treatment tank. As the selectively permeable 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 The following can be used.

[0005] Japanese Patent Publication No. 2023-54889 Japanese Patent Publication No. 2015-34315

[0006] To increase the amount of lithium recovered, reducing the resistance and increasing the area of ​​the electrolyte membrane are effective. However, existing solid electrolyte membranes made of ceramics are prone to cracking, limiting their thinning and increasing their area, and thus failing to achieve sufficient lithium processing capacity. On the other hand, supporting the electrolyte membrane with a support substrate is conceivable, but when the support substrate contains tetragonal zirconia, the tetragonal zirconia undergoes a phase transformation to monoclinic in hot water, causing microcracks due to volume expansion. For example, if the generated cracks propagate to the electrolyte membrane, its density is lost, leading to problems such as solution leakage. The present invention aims to provide a lithium separation member equipped with an electrolyte membrane that is less prone to problems such as cracking of the electrolyte membrane, even when the support substrate contains tetragonal zirconia.

[0007] To solve the above problems, the present invention provides a lithium separation member comprising: a lithium ion conductor layer that selectively permeates lithium ions; a support substrate containing tetragonal zirconia that supports the lithium ion conductor layer; and an intermediate layer provided between the lithium ion conductor layer and the support substrate, having a higher monoclinic zirconia content than the support substrate. Furthermore, the present invention provides a lithium separation apparatus comprising: a lithium separation member which is a member that selectively permeates lithium ions; and a pair of electrodes arranged on each side of two main surfaces of the lithium separation member, wherein the lithium separation member comprises: a lithium ion conductor layer that selectively permeates lithium ions; a support substrate containing tetragonal zirconia that supports the lithium ion conductor layer; and an intermediate layer provided between the lithium ion conductor layer and the support substrate, having a higher monoclinic zirconia content than the support substrate. Furthermore, the present invention provides a method for manufacturing a lithium separation member, comprising: a first sheet preparation step of creating a first sheet that will be the basis for a lithium ion conductor dense 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 be the basis for a support substrate that supports the lithium ion conductor dense layer; a third sheet preparation step of creating a third sheet that will be the basis for an intermediate layer provided between the lithium ion conductor dense layer and the support substrate, having a higher monoclinic zirconia content than the support substrate; and a firing step of firing the first sheet, the second sheet, and the third sheet to form a lithium ion conductor dense layer, a support substrate, and an intermediate layer.

[0008] The objective is to provide a lithium separation member equipped with an electrolyte membrane, which is less prone to problems such as cracking of the electrolyte membrane, even when the supporting substrate contains tetragonal zirconia.

[0009] FIG. 1 is a diagram showing a lithium separation apparatus to which the present embodiment is applied. FIG. 1 is a diagram showing a first example of the lithium separation member according to the first embodiment. FIG. 2 is a diagram showing a case where the lithium separation member having the structure of FIG. 2 is formed into a cylindrical shape. FIG. 1 is a diagram showing a second example of the lithium separation member according to the first embodiment. FIG. 4 is a diagram showing a case where the lithium separation member of FIG. 4 has a front-back symmetric structure. (a) to (b) are diagrams showing the lithium separation member according to the second embodiment. (a) to (c) are diagrams when the lithium separation member of FIG. 6(a) is viewed from the direction VII, and are diagrams showing the shape of the opening of the through-hole. FIG. 6(b) is a diagram showing a case where the lithium separation member of FIG. 6(b) has a front-back symmetric structure. FIG. 1 is a diagram showing an example of a method for manufacturing the lithium separation member according to the first embodiment. FIG. 1 is a diagram showing an example of a method for manufacturing the lithium separation member according to the second embodiment. FIG. 1 is a diagram showing another example of the method for manufacturing the lithium separation member according to the second embodiment.

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

[0011] <Description of Lithium Separation Apparatus 1> FIG. 1 is a diagram showing a lithium separation apparatus 1 to which the present embodiment is applied. The illustrated lithium separation apparatus 1 separates lithium ions (Li ＋ ) from a lithium-containing solution and recovers them. The lithium separation apparatus 1 includes a lithium separation member 10, electrodes 20 and 30, and a solution tank 40. The lithium separation member 10 is a member capable of selectively transmitting lithium ions. The electrode 20 is a positive electrode, and the electrode 30 is a negative electrode. The solution tank 40 stores the lithium-containing solution and the recovery solution.

[0012] In this case, electrodes 20 and 30 are arranged on respective sides of the two main surfaces of the lithium separation member 10. Here, the "main surface" refers to a surface having a much larger area than other surfaces. In this case, as will be described in detail later, the electrodes 20 and 30 are plate-shaped with a layered structure, and the side surfaces occupy only a small area compared to the total surface area of the electrodes 20 and 30. Therefore, in this case, the main surfaces are the two surfaces, i.e., the front surface other than the side surfaces and the back surface of the electrodes 20 and 30. Then, a lithium-containing solution is placed on the side of the electrode 20 that serves as the positive electrode. The lithium-containing solution is prepared by refining a lithium resource. Examples of the lithium resource include seawater, roasting and water leachate of waste lithium ion batteries (waste LIBs), salt lake brine, geothermal brine, and the like. Further, as a recovery solution, for example, pure water or an aqueous lithium hydroxide solution is placed on the side of the electrode 30 that serves as the negative electrode. When a direct current voltage is applied between the electrodes 20 and 30, lithium ions pass through the lithium separation member 10 from the side of the positive electrode 20 and move to the side of the negative electrode 30. In contrast, other ions have difficulty passing through the lithium separation member 10. That is, the lithium separation member 10 can selectively transmit lithium ions and separate them from other ions.

[0013] Then, carbon dioxide (CO ２ ) is blown into the recovery solution, and lithium ions are precipitated as lithium carbonate (Li ２ CO ３ ) and can be recovered. Lithium carbonate is reused as a raw material for batteries.

[0014] <Description of Configuration of Lithium Separation Member 10> Next, the lithium separation member 10 will be described with reference to the first to second embodiments.

[0015] [First Embodiment] Figure 2 shows a first example of the lithium separation member 10 of the first embodiment. The lithium separation member 10 shown consists of a lithium ion conductor layer 11, an intermediate layer 12, and a support substrate 13. 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 ３ This 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 ２O-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 ０．４６ Lithium 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 13 is a support that supports the lithium ion conductor layer 11. The support substrate 13 mainly contains tetragonal zirconia. "Mainly contains" means that the support substrate 13 contains 70 wt% or more of tetragonal zirconia. Furthermore, tetragonal zirconia is, for example, tetragonal yttria-stabilized zirconia (YSZ). In this case, zirconia (ZrO ２ ) is used as a stabilizer (yttria: Y ２ O ３ A mixture containing ) in an amount of 1.5 mol% to 5.5 mol% can be used. The amount of yttrium oxide added is preferably 2.5 mol% to 5.0 mol%, and more preferably 3.0 mol% to 4.0 mol%. Within the above range, the strength of the support substrate 13 can be further increased and damage to the lithium separation member 10 can be further suppressed.

[0020] Furthermore, the support substrate 13 has a porous structure. That is, the support substrate 13 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. Next, the total area of ​​the solid portion and the total area of ​​the porosity portion composed of the support substrate 13 are determined from the analyzed cross section image. Next, the area occupancy rate of the porosity portion is calculated. This area occupancy rate of the porosity portion 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 13. Furthermore, the average pore diameter is preferably 0.1 μm to 50 μm. The average pore diameter is obtained by calculating the average equivalent circle diameter for each of the five cross-sectional images after the analysis described above, and then taking the arithmetic mean of the average equivalent circle diameters for each of the five cross-sectional images. 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 13 porous, lithium can be separated when the raw solution or recovered solution permeates the support substrate 13 and comes into contact with the lithium ion conductor layer 11. The thickness of the support substrate 13 is preferably 0.5 mm or more and 10 mm or less. If the thickness of the support substrate 13 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 13 exceeds 10 mm, the resistance increases and the lithium separation performance tends to decrease.

[0021] By providing the support substrate 13, the strength of the lithium separation member 10 is improved, and crack formation in the lithium ion conductor layer 11 can be suppressed. Furthermore, since the strength can be ensured by the support substrate 13, 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.

[0022] The intermediate layer 12 is provided between the lithium-ion conductor layer 11 and the support substrate 13, and is a functional layer that suppresses crack formation in the lithium-ion conductor layer 11. The support substrate 13 mainly contains tetragonal zirconia, but tetragonal zirconia undergoes a phase transformation from tetragonal to monoclinic in hot water, and fine cracks may occur due to volume expansion. Since the degradation of tetragonal zirconia progresses from the surface in contact with hot water, by designing the support substrate 13 appropriately while taking degradation into consideration, the impact of the decrease in strength of the support substrate 13 can be reduced when the degree of degradation is small. However, if the lithium-ion conductor layer 11 and the support substrate 13 are in direct contact, even when the degree of degradation is small, fine cracks that occur near the lithium-ion conductor layer 11 in the support substrate 13 may propagate to the lithium-ion conductor layer 11. In this case, the density of the lithium-ion conductor layer 11 is lost, and a problem of solution leakage occurs. Therefore, in this embodiment, an intermediate layer 12 is provided between the lithium-ion conductor layer 11 and the support substrate 13, thereby suppressing the occurrence of cracks in the lithium-ion conductor layer 11 even if fine cracks occur in the support substrate 13. Furthermore, the overall strength of the lithium separation member 10 is guaranteed by the support substrate 13, so its strength is also high. In this case, the intermediate layer 12 can also be considered as a crack suppression layer or buffer layer that suppresses the occurrence of cracks in the lithium-ion conductor layer 11.

[0023] The intermediate layer 12 contains monoclinic zirconia. The intermediate layer 12 has a higher monoclinic zirconia content than the support substrate 13. Monoclinic zirconia can be, for example, zirconia without stabilizers, monoclinic zirconia with a small amount of yttrium oxide added, or yttria-stabilized zirconia with added lithium to form a monoclinic crystal. However, it is not limited to these, and any composition of monoclinic zirconia is acceptable. The component other than monoclinic zirconia can be, for example, tetragonal zirconia. Monoclinic zirconia does not undergo a phase change when exposed to hot water, so it does not expand in volume. Therefore, by providing a layer containing monoclinic zirconia as the intermediate layer 12, it is possible to suppress the occurrence of cracks in the lithium ion conductor layer 11.

[0024] If the intermediate layer 12 is a mixture of monoclinic zirconia and tetragonal zirconia, the proportion of each can be determined from the intensity ratio of the Raman spectrum. In this embodiment, the respective content refers to the ratio of monoclinic zirconia or tetragonal zirconia to the total amount of tetragonal zirconia and monoclinic zirconia, and this is directly determined from the intensity ratio of the Raman spectrum. For example, the Raman spectrum intensity ratio is calculated by analyzing the Raman spectrum of the intermediate layer 12 using the Raman spectrum specific to each material. In this case, it is preferable to calculate the average value of the proportion derived from each material by analyzing the Raman spectra obtained from 10 or more arbitrary locations in the intermediate layer 12.

[0025] The intermediate layer 12 preferably contains 10% or more monoclinic zirconia. If the monoclinic zirconia content is less than 10%, the effect of suppressing volume expansion and microcracks will be reduced, and cracks may propagate to the lithium ion conductor layer 11. The intermediate layer 12 may also be 100% monoclinic zirconia. The intermediate layer 12 preferably has a thickness of 5 μm or more and 100 μm or less. If the thickness of the intermediate layer 12 is less than 5 μm, the effect as a buffer layer will be difficult to obtain, and cracks may propagate to the lithium ion conductor layer 11 if the deterioration of the support substrate 13 progresses. Also, if the thickness of the intermediate layer 12 exceeds 100 μm, fine cracks may occur in the intermediate layer 12 after firing. The boundary between the intermediate layer 12 and the support substrate 13 can be defined by analysis of the cross-section by Raman spectroscopy. First, Raman spectral analysis is performed on the cross-section of the support substrate 13 to determine the monoclinic zirconia content. Next, by continuously performing Raman spectral analysis in the thickness direction, a line was determined at which the proportion of monoclinic zirconia exceeded the monoclinic zirconia oil content of the support substrate 13. This line was used as a boundary to distinguish the intermediate layer 12 from the support substrate 13. The distance between this boundary and the boundary between the lithium ion conductor layer 11 and the intermediate layer 12 was defined as the thickness of the intermediate layer 12.

[0026] Furthermore, components other than monoclinic zirconia and tetragonal zirconia can also be lithium ion conductors. In other words, the intermediate layer 12 further contains components that constitute the lithium ion conductor layer 11. Specifically, the components of the intermediate layer 12 can be, for example, monoclinic zirconia, tetragonal zirconia, and lithium lanthanum titanate (LLTO). The total mixing ratio of the lithium ion conductor, tetragonal zirconia, and monoclinic zirconia can be 10% to 90% by volume. Preferably, the total mixing ratio of the lithium ion conductor, tetragonal zirconia, and monoclinic zirconia is 20% to 80%, and more preferably 30% to 70%. By making the intermediate layer 12 such components, the adhesive strength between the lithium ion conductor layer 11 and the support substrate 13 can be improved and peeling can be suppressed. In this case, the intermediate layer 12 can also be considered as an adhesive layer that bonds the lithium ion conductor layer 11 and the support substrate 13.

[0027] Furthermore, the intermediate layer 12 has a porous structure similar to that of the support substrate 13. The porosity of the intermediate layer 12 is preferably 20% to 60%. The average pore diameter is preferably 0.1 μm to 50 μm. The porosity and average pore diameter of the intermediate layer 12 are measured in the same manner as the support substrate 13 described above. The lithium separation member 10 of this embodiment can be rectangular, for example, in which case its size is, for example, 50 mm to 300 mm. Alternatively, the shape may be disc-shaped, in which case its size is, for example, 50 mm to 300 mm. Conventionally, the size of the lithium separation member 10 has been limited to about 50 mm or 50 mm at most, so it is possible to increase the area compared to 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 recovered liquid can be increased compared to using a plate-shaped lithium separation member, thereby improving the lithium recovery efficiency. Furthermore, forming it into a cylindrical shape allows for greater strength compared to a plate-like shape.

[0028] 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 13 is cylindrical on the inside, so that the overall shape is also cylindrical. The intermediate layer 12 is also cylindrical and is provided between the lithium ion conductor layer 11 and the support base material 13. 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 liquid or recovered liquid and the lithium separation member 10 is increased, a sufficient amount of liquid can be passed through the cylinder, and the recovery efficiency of lithium contained in the raw liquid 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, thereby improving the recovery efficiency of lithium contained in the raw solution. There is no particular upper limit to the length, but for example, it should be 2000 mm or less, and typically it is 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 solution or recovered solution.

[0029] Figure 4 shows a second example of the lithium separation member 10 of the first 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.

[0030] 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).

[0031] The lithium-ion conductor porous layer 112 is positioned between the lithium-ion conductor dense layer 111 and the intermediate layer 12, and has a porous structure. Specifically, 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 manner as the support substrate 13 described above. By making the lithium-ion conductor porous layer 112 porous, the surface area of ​​the lithium-ion conductor layer 11 is increased, resulting in lower resistance. This also makes it 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 less pronounced. 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.

[0032] The support substrate 13 is the same as in Figure 2. That is, the main component of the support substrate 13 is tetragonal zirconia, for example, tetragonal yttria-stabilized zirconia (YSZ). The intermediate layer 12 is also the same as in Figure 2. That is, the intermediate layer 12 contains monoclinic zirconia. The components other than monoclinic zirconia can be, for example, tetragonal zirconia. The components other than monoclinic zirconia are, for example, the components that make up the lithium ion conductor layer 11 and the components that make up the support substrate 13, for example, tetragonal zirconia and lithium lanthanum titanate (LLTO).

[0033] In the case of Figure 4, although the lithium-ion conductor layer 11 and the support substrate 13 are not in direct contact, if the tetragonal zirconia contained in the support substrate 13 undergoes a phase transformation from tetragonal to monoclinic, resulting in volume expansion and the formation of fine cracks, these cracks will propagate and cause cracks in the lithium-ion conductor porous layer 112. These cracks will sever the ion conduction path, leading to a reduction in the effective area. In other words, the effect of increasing the surface area of ​​the lithium-ion conductor layer 11 and reducing resistance, as described above, is diminished. Therefore, in this embodiment, an intermediate layer 12 is provided between the lithium-ion conductor porous layer 112 and the support substrate 13. This suppresses the formation of cracks in the lithium-ion conductor porous layer 112 even if fine cracks form in the support substrate 13. In this case, the intermediate layer 12 can also be considered a crack suppression layer or buffer layer that suppresses the formation of cracks in the lithium-ion conductor porous layer 112.

[0034] Figure 5 shows the lithium separation member 10 of Figure 4 with a front-to-back symmetrical structure. The lithium separation member 10 shown is laminated in the following order: support base material 13, intermediate layer 12, lithium ion conductor porous layer 112, lithium ion conductor dense layer 111, lithium ion conductor porous layer 112, intermediate layer 12, and support base material 13. In other words, the lithium ion conductor dense layer 111 is sandwiched between the lithium ion conductor porous layer 112, intermediate layer 12, and support base material 13, 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 5; for example, the lithium separation member 10 shown in Figures 2 and 3 may also have a front-to-back symmetrical structure.

[0035] [Second Embodiment] In the first embodiment, the support base material 13 had a porous structure, but in the second embodiment, the support base material 13 has a dense structure with multiple through holes. Figures 6(a) and 6(b) show the lithium separation member 10 of the second embodiment. Of these, Figure 6(a) shows the case where the support base material 13 of the lithium separation member 10 shown in Figure 2 has the structure of the second embodiment. Similarly, Figure 6(b) shows the case where the support base material 13 of the lithium separation member 10 shown in Figure 4 has the structure of the second embodiment.

[0036] In the second embodiment, the support substrate 13 has a dense structure, so its porosity is low, less than 10%. Furthermore, the support substrate 13 has a plurality of through holes 13h. In this case, the through holes 13h are holes that penetrate from one main surface of the support substrate 13 to the other main surface, and openings 13k are formed on both the one main surface and the other main surface of the support substrate 13. By providing the through holes 13h, lithium can be separated when the raw liquid or recovered liquid enters the through holes 13h and comes into contact with the lithium ion conductor layer 11.

[0037] Figures 7(a) to 7(c) show the lithium separation member 10 of Figures 6(a) to 6(b) as viewed from direction VII, and illustrate the shape of the opening 13k of the through hole 13h. Of these, Figures 7(a) to 7(b) show the case where the shape of the opening 13k is circular. Figure 7(a) shows the case where multiple openings 13k are arranged in a grid pattern, and Figure 7(b) shows the case where multiple openings 13k are arranged in a staggered pattern. Figure 7(c) shows the case where the shape of the opening 13k is rectangular. Note that the shape of the opening 13k is not limited to these. For example, it may be elliptical, triangular, hexagonal, or other polygonal shape, or it may be irregular in shape. Also, the multiple openings 13k do not need to be the same shape, and multiple shapes may be mixed. Furthermore, the arrangement of the through holes 13h is not limited to these. For example, they may be arranged randomly, or the arrangement may be partially changed, such as being different in the center and on the outer periphery. Also, when the shape of the opening 13k is rectangular, the corners may be chamfered. In this case, the chamfer may be an R-chamfer or a C-chamfer. In the case of an R-chamfer, it is preferable that the radius of curvature be 0.5 mm or more.

[0038] The size W1 of the opening 13k of the through hole 13h is preferably 15 mm or less. Furthermore, the size W1 of the opening 13k is preferably such that W1 / thickness of the support base material 13 is 1 or more. Here, the size W1 of the opening 13k is the maximum dimension of the opening 13k. Therefore, in the cases of Figures 7(a) to (b), the size W1 of the opening 13k is the length of the diameter of the circle. Also, in the case of Figure 7(c), the size W1 of the opening 13k is the length of the diagonal of the rectangle. If the size W1 of the opening 13k exceeds 15 mm, the area on which the lithium ion conductor layer 11 stands independently becomes large, resulting in insufficient strength of the lithium ion conductor layer 11 and making it prone to failure. Furthermore, if the thickness W1 / thickness of the support base material 13 is less than 1, the resistance tends to increase due to a decrease in the exposed area of ​​the lithium ion conductor layer 11 and the accumulation of air bubbles within the through hole 13h.

[0039] In this embodiment, the support base material 13 has a frame portion 13s on the outer circumference of the main surface, which is a region where through holes 13h are not formed. The frame portion 13s is the region outside the line drawn so as to be in contact with the outermost through hole 13h, and having a shape similar to the outer shape of the lithium separation member 10. In Figures 7(a) to (c), the outer shape of the lithium separation member 10 is rectangular, and the frame portion 13s is the region outside the rectangle shown by the dotted line in the figure. By providing the frame portion 13s, the strength of the support base material 13 can be improved while maintaining recovery efficiency. The width W2 of the frame portion 13s is preferably 0.5 mm or more. If the width W2 of the frame portion 13s is less than 0.5 mm, the strength of the support base material 13 will decrease, and the lithium separation member 10 will be more prone to damage. Furthermore, the width W2 of the frame portion 13s is preferably 14% or less of the outer dimensions of the support base material 13. If the width W2 of the frame portion 13s exceeds 14% of the outer dimensions of the support base material 13, the effective area having the opening 13k decreases, and the size of the lithium separation device 1 becomes large relative to the lithium processing capacity, resulting in significant space loss. The opening ratio of the through holes 13h in the region where the through holes 13h are formed, excluding the frame portion 13s, is preferably 25% to 95%. The region where the through holes 13h are formed is the region inside the dotted line in the figure. If the opening ratio exceeds 95%, the strength of the support base material 13 decreases, and the lithium separation member 10 becomes more susceptible to damage. Also, if the opening ratio is less than 25%, the exposed area of ​​the lithium ion conductor layer 11 decreases, and the effect of increased resistance due to the reduced exposed area becomes greater than the effect of resistance reduction due to thinning. The width W3 of the crossbar, which is the shortest distance between adjacent through holes 13h in the region where the through holes 13h are formed, excluding the frame portion 13s, is preferably 0.05 mm to 3 mm. If the width W3 of the crossbar exceeds 3 mm, the exposed area of ​​the lithium ion conductor layer 11 decreases, and the effect of increased resistance due to the reduced exposed area becomes greater than the effect of resistance reduction due to thinning. Also, if the width W3 of the crossbar is less than 0.05 mm, the strength of the support base material 13 decreases, and the lithium separation member 10 becomes more susceptible to damage. It is preferable that the width W2 of the frame portion 13s is greater than the width W3 of the crossbar, which is the shortest distance between adjacent through holes 13h in the region where the through holes 13h are formed excluding the frame portion 13s.

[0040] Furthermore, through-holes may also be formed in the intermediate layer 12. In this case, the through-holes 13h of the support substrate 13 are formed to extend into the intermediate layer 12, so as to penetrate both the support substrate 13 and the intermediate layer 12. In this case, the intermediate layer 12 does not have a porous structure and can be a dense layer. In other words, by providing through-holes in the intermediate layer 12, the raw liquid or recovered liquid can penetrate these through-holes, so it is not necessary to make it porous.

[0041] The lithium separation member 10 of the second embodiment can also have a front-to-back symmetrical structure. Figure 8 shows the lithium separation member 10 of Figure 6(b) with a front-to-back symmetrical structure. The lithium separation member 10 shown is laminated in the following order: support base material 13, intermediate layer 12, lithium ion conductor porous layer 112, lithium ion conductor dense layer 111, lithium ion conductor porous layer 112, intermediate layer 12, and support base material 13. In other words, the lithium ion conductor dense layer 111 is sandwiched between the lithium ion conductor porous layer 112, intermediate layer 12, and support base material 13, which are laminated in the vertical direction in the figure, resulting in a front-to-back symmetrical structure. Furthermore, through holes 13h are formed in each of the support base materials 13.

[0042] <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 a manufacturing method of the lithium separation member 10 of the first embodiment. Here, the lithium separation member 10 is manufactured by producing corresponding green sheets by tape molding, laminating these green sheets, and then applying pressure and firing. Note that Figure 9 illustrates the manufacturing of the lithium separation member 10 with the structure of Figure 2.

[0043] (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.

[0044] (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 lithium ion conductor porous layer 112 can be controlled by adjusting the amount of pore-forming material added, and the pore size of the lithium ion conductor porous layer 112 can be controlled by adjusting the particle size of the pore-forming material.

[0045] (Preparation of the intermediate layer 12 green sheet) The intermediate layer 12 green sheet may be manufactured by any method, but for example, it can be manufactured as follows. First, an intermediate layer slurry is prepared by mixing tetragonal zirconia powder, monoclinic 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 intermediate layer 12 green sheet. At this time, the thickness of the intermediate layer 12 green sheet can be adjusted by adjusting the coating thickness. In addition, the porosity of the intermediate layer 12 can be controlled by adjusting the amount of pore-forming agent added, and the pore size of the intermediate layer 12 can be controlled by adjusting the particle size of the pore-forming agent.

[0046] (Preparation of the support substrate 13 green sheet) The support substrate 13 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 tetragonal 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 13. At this time, the thickness of the support substrate 13 green sheet can be adjusted by adjusting the coating thickness. In addition, the porosity of the support substrate 13 can be controlled by adjusting the amount of pore-forming agent added, and the pore diameter of the support substrate 13 can be controlled by adjusting the particle size of the pore-forming agent.

[0047] (Cutting / Lamination) 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 performed 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 and 4 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 intermediate layer 12, and the support substrate 13 can be controlled by adjusting the thickness and number of layers of each layer of green sheet.

[0048] (Firing) The laminated green sheets are then 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, the green sheets that will become the intermediate layer 12, and the green sheets that will become the support substrate 13 are fired together (co-firing), and each becomes the lithium ion conductor dense layer 111, the intermediate layer 12, and the support substrate 13, respectively. In this way, a lithium separation member 10 can be manufactured in which the lithium ion conductor dense layer 111, the intermediate layer 12, and the support substrate 13 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, the intermediate layer 12, and the support substrate 13 and firing them together, but the lithium ion conductor dense layer 111, the intermediate layer 12, and the support substrate 13 may be manufactured by firing them sequentially or separately. Specifically, the green sheet that will form the intermediate layer 12 and the green sheet that will form the support base material 13 are laminated together, and the laminate that will form the intermediate layer 12 and the support base material 13 is fired once to manufacture the intermediate layer 12 and the support base material 13. Then, the green sheet that will form the lithium ion conductor dense layer 111 may be laminated onto the manufactured intermediate layer 12 and fired. Furthermore, the green sheet that will form the intermediate layer 12 may be laminated onto the support base material 13 together with the green sheet that will form the lithium ion conductor dense layer 111 after the support base material 13 has been manufactured and fired. Alternatively, the green sheet that will form the lithium ion conductor dense layer 111 and the green sheet that will form the intermediate layer 12 may be fired separately, and the manufactured lithium ion conductor dense layer 111, intermediate layer 12 and support base material 13 may be joined together.

[0049] Figure 10 shows an example of a manufacturing method for the lithium separation member 10 of the second embodiment. Figure 10 illustrates the manufacturing of the lithium separation member 10 with the structure shown in Figure 6(a). The manufacturing method for the lithium separation member 10 shown in Figure 10 involves creating green sheets to form each layer, and then cutting and laminating them. At this time, the green sheets to form each layer are created in the same manner as in Figure 9, except that a por-forming agent is not added to the zirconia slurry for creating the support base material 13.

[0050] (Punching) After laminating the green sheets, multiple through holes 13h are formed in the laminate of green sheets that will form the base material 13 by punching. The size, arrangement, and shape of the openings 13k of the through holes 13h are determined by the die used for punching. Punching can be performed by any known method and is not particularly limited, but a punching machine or a press machine can be used.

[0051] (Lamination) Then, the green sheets that will form the intermediate layer 12 and the green sheets that will form the lithium-ion conductor dense layer 111 are laminated onto the laminate of green sheets that will form the base material 13 that has been punched out. At this time, the structures shown in Figures 6(a) to (b) can be created depending on the type of green sheet to be laminated. If through holes are to be provided in the intermediate layer 12, the through holes can be formed by laminating the green sheet that will form the intermediate layer 12 together with the green sheet that will form the base material 13 and then punching it out. Furthermore, the thickness of the lithium-ion conductor dense layer 111, the lithium-ion conductor porous layer 112, and the intermediate layer 12 can be controlled by adjusting the thickness of the green sheets in each layer and the number of layers.

[0052] (Firing) Next, the laminated green sheets are cut to a predetermined shape and size and fired (1150 to 1500°C, 1 to 10 hours). That is, the green sheets that will become the lithium ion conductor dense layer 111, the green sheets that will become the intermediate layer 12, and the green sheets that will become the support substrate 13 are fired together (co-firing), and each becomes the lithium ion conductor dense layer 111, the intermediate layer 12, and the support substrate 13, 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 13 are laminated, for example, as shown in Figure 6(a). 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, the intermediate layer 12, and the support substrate 13 and firing them together, but the lithium ion conductor dense layer 111, the intermediate layer 12, and the support substrate 13 may be manufactured by firing them sequentially or separately.

[0053] In the above process, punching was performed after cutting / lamination, but there is also a method in which the green sheet that will become the support base material 13 is punched first, and then cutting / lamination is performed. In this case, the second lamination is unnecessary. Also, in the above process, through holes 13h were formed by punching, but this is not the only method. For example, through holes 13h can be formed by laser processing.

[0054] Figure 11 shows another example of the manufacturing method for the lithium separation member 10 of the second embodiment. Here, the manufacturing method for the lithium ion conductor dense layer 111 is the same, but the manufacturing method for the support substrate 13 is different, so only the manufacturing method for the support substrate 13 is shown before the lamination and firing processes. In Figure 11, the support substrate 13 is not made from a green sheet, but from a piece that has been extruded and cut.

[0055] (Extrusion molding, cutting) First, zirconia clay is prepared by kneading tetragonal zirconia powder, a dispersant, a solvent, a plasticizer, and a binder. Then, this zirconia clay is put into an extrusion molding machine and a molded body is manufactured by extrusion molding through a square-shaped die. The die has an opening shape for forming multiple through holes 13h. The extrusion molding is carried out in a direction such that the direction in which the through holes 13h extend is horizontal. At this time, by making the shape of the die square, a rectangular parallelepiped molded body as shown in Figure 11 can be produced. After extrusion molding, it is cut to a predetermined length by a cutting means such as a wire cutter.

[0056] (Lamination and firing) After this, the process is the same as in Figure 10, and the green sheet that will become the intermediate layer 12 and the green sheet that will become the lithium ion conductor dense layer 111 are laminated onto the cut molded body and fired (1150 to 1500°C, 1 to 10 hours). Alternatively, the support base material 13 may be fired first, and the green sheet that will become the lithium ion conductor dense layer 111 and the green sheet that will become the intermediate layer 12 may be laminated onto the manufactured support base material 13 and fired, or the green sheet that will become the lithium ion conductor dense layer 111 and the green sheet that will become the intermediate layer 12 may be fired separately, and the manufactured lithium ion conductor dense layer 111, intermediate layer 12 and support base material 13 may be joined together. In this case, the extruded columnar support base material 13 may be fired and then cut to a predetermined thickness.

[0057] The manufacturing method for the lithium separation member 10 shown in Figures 9 to 11 can be understood as a manufacturing method for 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 contains a lithium ion conductor that selectively permeates lithium ions and has a dense structure; a second sheet creation step of creating a second sheet (in this case, a green sheet that will become the support base material 13) which supports the lithium ion conductor dense layer 111 and will become the support base material 13; a third sheet creation step of creating a third sheet (in this case, a green sheet that will become the intermediate layer 12) which is provided between the lithium ion conductor dense layer 111 and the support base material 13 and will become the intermediate layer 12 which contains monoclinic zirconia; and a firing step of firing the first sheet, the second sheet, and the third sheet to form the lithium ion conductor dense layer 111, the support base material 13, and the intermediate layer 12.

[0058] Examples of the present invention will be described below. In these examples, lithium-ion conductive solid electrolyte ceramics (LLTO) were used as the lithium-ion conductor. The support substrate 13 was made of 3.0 mol% yttria-stabilized zirconia (3YSZ). Table 1 below shows the manufacturing conditions and evaluation results for Examples 1 to 19 and Comparative Examples 1 to 2.

[0059]

[0060] [Examples 1-11, 16-17] In Examples 1-11 and 16-17, the lithium separation member 10 shown in Figure 2 was fabricated.

[0061] (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.

[0062] (Preparation of the green sheet that will become the intermediate layer 12) First, an intermediate layer slurry was prepared by mixing monoclinic zirconia powder, 3YSZ powder, a dispersant, a solvent, a plasticizer, a binder, and polymethyl methacrylate beads as a pore-forming material. The prepared intermediate layer slurry was formed into a sheet on a PET film using the doctor blade method to form a green sheet that will become the intermediate layer 12. At this time, the thickness of the green sheet and the mixing ratio of monoclinic zirconia powder and 3YSZ powder were adjusted to create Examples 1 to 11 and 16 to 17. The thickness and composition of the intermediate layer 12 after firing the green sheet are shown in Table 1. In Examples 5, 9, and 16, the intermediate layer 12 was formed directly on the green sheet of the support substrate 13 by the printing method. In other words, in Examples 1 to 4, the thickness of the intermediate layer 12 was 10 μm, and the monoclinic zirconia content in the intermediate layer 12 was 10%, 30%, 60%, and 100%, respectively. Furthermore, in Examples 5 to 8, the monoclinic zirconia content in the intermediate layer 12 was set to 30%, and the thickness of the intermediate layer 12 was set to 5 μm, 20 μm, 50 μm, and 100 μm, respectively. On the other hand, in Examples 9 to 11, the monoclinic zirconia content in the intermediate layer 12 was set to 10%, and the thickness of the intermediate layer 12 was set to 5 μm, 10 μm, and 20 μm, respectively. In addition, in Examples 16 to 17, the monoclinic zirconia content in the intermediate layer 12 was set to 30%, and the thickness of the intermediate layer 12 was set to 2 μm and 120 μm, respectively.

[0063] (Preparation of the green sheet that will become the support substrate 13) 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 13. The thickness of this green sheet was formed to be 200 μm after firing. In Examples 1 to 8 and 16 to 17, the monoclinic zirconia content in the support substrate 13 was set to 0%. In Examples 9 to 11, monoclinic zirconia powder was mixed in to a content of 5%.

[0064] (Lamination, Pressing, and Firing) One green sheet to form the lithium-ion conductor dense layer 111, one green sheet to form the intermediate layer 12, and ten green sheets to form the support substrate 13 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 1350°C for 2 hours in air to obtain the lithium separation member 10 shown in Figure 2. Two of each lithium separation member 10 were prepared.

[0065] [Examples 12-15] In Examples 12-15, the lithium separation member 10 shown in Figure 6(a) was fabricated.

[0066] [Examples 18-19] In Examples 18-19, the support substrate 13 was 4.0 mol% yttria-stabilized zirconia (4YSZ) and 5.0 mol% yttria-stabilized zirconia (5YSZ), respectively.

[0067] (Preparation of green sheets to form each layer) In Examples 12 to 15, green sheets to form each layer were prepared and cut / laminated. At this time, the green sheets to form each layer were prepared in the same manner as in Examples 1 to 11 and 16 to 17, except that no pore-forming agent was added to the zirconia slurry for creating the intermediate layer 12 and the support base material 13. In Examples 12 to 15, the monoclinic zirconia content in the support base material 13 was set to 0%. The thickness of the intermediate layer 12 was set to 10 μm, and the monoclinic zirconia content in the intermediate layer 12 was set to 10%, 30%, 60%, and 100%, respectively. Multiple through holes 13h were formed in the laminate of green sheets to form the intermediate layer 12 and the support base material 13 by punching. The shape of the through holes 13h was circular, and the size W1 of the opening 13k and the width W3 of the crossbar after firing were set to 2.5 mm and 0.5 mm, respectively.

[0068] (Lamination, Pressing, and Firing) One green sheet to form the lithium-ion conductor dense layer 111, one green sheet to form the intermediate layer 12, and ten green sheets to form the punched support base material 13 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 bonded 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 in air at 1350°C for 2 hours to obtain the lithium separation member 10 shown in Figure 6(a).

[0069] [Comparative Example 1] In Comparative Example 1, the lithium separation member was prepared in the same manner as in Example 1, except that the intermediate layer 12 was not provided. In this case, the lithium separation member has a structure in which the intermediate layer 12 is removed from the lithium separation member 10 shown in Figure 2.

[0070] [Comparative Example 2] In Comparative Example 2, the lithium separation member was prepared in the same manner as in Example 12, except that the intermediate layer 12 was not provided. In this case, the lithium separation member has a structure in which the intermediate layer 12 is removed from the lithium separation member 10 shown in Figure 6(a).

[0071] [Comparative Example 3] In Comparative Example 3, the lithium separation member was prepared in the same manner as in Example 19, except that the intermediate layer 12 was not provided. In this case, the lithium separation member has a structure in which the intermediate layer 12 is removed from the lithium separation member 10 shown in Figure 6(a).

[0072] [Comparative Example 4] In Comparative Example 4, the lithium separation member was prepared in the same manner as in Example 20, except that the intermediate layer 12 was not provided. In this case, the lithium separation member has a structure in which the intermediate layer 12 is removed from the lithium separation member 10 shown in Figure 6(a).

[0073] (Evaluation Method) First, the cross-section of one of the obtained lithium separation members 10 was observed using an SEM to check for the presence or absence of fine cracks in the intermediate layer 12. This allowed for confirmation of the presence or absence of fine cracks in the intermediate layer 12 in its initial state. Next, the durability of the remaining lithium separation members 10 was evaluated by an accelerated degradation test. Specifically, in Examples 1 to 17 and Comparative Examples 1 to 2, the lithium separation members 10 were immersed in hot water at 140°C for 60 hours. In Example 18 and Comparative Example 3, the lithium separation members 10 were immersed in hot water at 140°C for 120 hours, and in Example 19 and Comparative Example 4, the lithium separation members 10 were immersed in hot water at 140°C for 240 hours. After the accelerated degradation test, the cross-section of the lithium separation member 10 was observed using an SEM to check for the presence or absence of fine cracks in the lithium ion conductor dense layer 111. At this time, samples without cracks were marked with ○, samples with cracks penetrating the lithium-ion conductor layer 111 were marked with ×, and samples with fine cracks that did not penetrate the lithium-ion conductor layer 111 were marked with △.

[0074] (Results) Examples 1 to 19, which included an intermediate layer 12 with a high monoclinic zirconia content, were able to reduce the fine cracks that occurred in the lithium-ion conductor dense layer 111 after the accelerated degradation test compared with Comparative Examples 1 to 4. Furthermore, Examples 1 to 15 and 17 to 19, in which the thickness of the intermediate layer 12 was 5 μm or more, were able to suppress the occurrence of cracks in the lithium-ion conductor dense layer 111 itself. Examples 1 to 16 and 18 to 19, in which the thickness of the intermediate layer 12 was 100 μm or less, were able to suppress the initial fine cracks in the intermediate layer 12. On the other hand, in Comparative Examples 1 to 4, cracks occurred in the lithium-ion conductor dense layer 111 during the accelerated degradation test, and there was a possibility that problems would arise with long-term use depending on the operating conditions of the lithium separation device 1.

[0075] 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.

[0076] 1...Lithium separation device, 10...Lithium separation member, 11...Lithium ion conductor layer, 12...Intermediate layer, 13...Support base material, 13h...Through hole, 13k...Opening, 13s...Frame part, 111...Lithium ion conductor dense layer, 112...Lithium ion conductor porous layer

Claims

1. A lithium separation member comprising: a lithium ion conductor layer that selectively permeates lithium ions; a support substrate containing tetragonal zirconia that supports the lithium ion conductor layer; and an intermediate layer provided between the lithium ion conductor layer and the support substrate, having a higher monoclinic zirconia content than the support substrate.

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 intermediate layer and having a porous structure.

4. The lithium separation member according to any one of claims 1 to 3, wherein the intermediate layer includes components constituting the lithium ion conductor layer.

5. The lithium separation member according to any one of claims 1 to 3, wherein the intermediate layer comprises tetragonal zirconia.

6. The lithium separation member according to claim 1, wherein the support base material has a porous structure.

7. The lithium separation member according to claim 1, wherein the support base material has a dense structure having a plurality of through holes.

8. The lithium separation member according to claim 1, wherein the monoclinic zirconia content of the intermediate layer is 10% or more.

9. The lithium separation member according to claim 1, wherein the intermediate layer has a thickness of 5 μm or more and 100 μm or less.

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

11. A lithium separation apparatus comprising: a lithium separation member which is a member that selectively allows lithium ions to pass through; and a pair of electrodes arranged on each side of two main surfaces of the lithium separation member, wherein the lithium separation member comprises: a lithium ion conductor layer which selectively allows lithium ions to pass through; a support substrate which supports the lithium ion conductor layer and contains tetragonal zirconia; and an intermediate layer provided between the lithium ion conductor layer and the support substrate, having a higher monoclinic zirconia content than the support substrate.

12. A method for manufacturing a lithium separation member, comprising: a first sheet preparation step of creating a first sheet that will be the basis for a lithium ion conductor dense 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 be the basis for a support substrate that supports the lithium ion conductor dense layer; a third sheet preparation step of creating a third sheet that will be the basis for an intermediate layer provided between the lithium ion conductor dense layer and the support substrate, having a higher monoclinic zirconia content than the support substrate; and a firing step of firing the first sheet, the second sheet and the third sheet to form the lithium ion conductor dense layer, the support substrate and the intermediate layer.

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