JP2016139535A - Method for evaluating hydroxide ion conductive dense membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method with which it is possible to evaluate reliably with high accuracy whether or not a hydroxide ion conductive dense membrane has sufficiently high compactness suitable for a prescribed purpose of use such as a separator for batteries, etc. (especially for zinc secondary batteries in which zinc dendrite growth presents a problem).SOLUTION: Provided is a method for evaluating the compactness of a hydroxide ion conductive dense membrane, the method including: a step for making a first aqueous solution including Zn contact one surface of the hydroxide ion conductive dense membrane and making a second aqueous solution not including Zn or water contact the other surface of the hydroxide ion conductive dense membrane, and making Zn permeate the dense membrane for a prescribed time; and a step for calculating a Zn permeation ratio by the expression (C×V)/(C×V×t×S) using the Zn concentration Cof the first aqueous solution before Zn permeation starts, the liquid quantity Vof the first aqueous solution before Zn permeation starts, the Zn concentration Cof the second aqueous solution or water after Zn permeation has ended, the liquid quantity Vof the second aqueous solution or water after Zn permeation has ended, and the duration t of Zn permeation, and a membrane area S that Zn permeates.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to a method for evaluating the denseness of a hydroxide ion conductive dense membrane.

  Layered Double Hydroxide (hereinafter also referred to as LDH) typified by hydrotalcite is a group of substances having anions that can be exchanged between hydroxide layers. It is used as a catalyst, an adsorbent, and a dispersant in a polymer for improving heat resistance. In particular, in recent years, it has been attracting attention as a material that conducts hydroxide ions, and addition to an electrolyte of an alkaline fuel cell or a catalyst layer of a zinc-air cell has also been studied.

  When considering catalysts and the like which are conventional application fields, synthesis and use in powdered LDH was sufficient because a high specific surface area was required. On the other hand, when considering application to an electrolyte utilizing hydroxide ion conductivity such as an alkaline fuel cell, a highly dense LDH film is desirable in order to prevent mixing of fuel gas and obtain sufficient electromotive force. It is.

  Patent Documents 1 and 2 and Non-Patent Document 1 disclose an oriented LDH film. The oriented LDH film suspends the surface of a polymer base material horizontally in a solution containing urea and a metal salt to nucleate LDH. It is produced by forming and orientation growing. In each of the X-ray diffraction results of the oriented LDH thin films obtained in these documents, a strong peak of (003) plane is observed.

  By the way, although zinc secondary batteries, such as a nickel zinc secondary battery and a zinc air secondary battery, have been developed and studied for a long time, they have not yet been put into practical use. This is because the zinc constituting the negative electrode produces dendritic crystals called dendrite during charging, and this dendrite breaks through the separator and causes a short circuit with the positive electrode. Therefore, a technique for preventing a short circuit due to zinc dendrite in a zinc secondary battery such as a nickel zinc secondary battery or a zinc-air secondary battery is strongly desired.

Chinese registered patent gazette CNC 1333113 International Publication No. 2006/050648

Zhi Lu, Chemical Engineering Science 62, pp. 6069-6075 (2007), “Microstructure-controlled synthesis of oriented layered double hydroxide thin films: Effect of varying the preparation conditions and a kinetic and mechanistic study of film formation”

  The present inventors have succeeded in producing a dense bulk body of LDH (hereinafter referred to as an LDH dense body). In addition, while conducting evaluation of hydroxide ion conductivity for LDH dense bodies, it has been found that high conductivity is exhibited by conducting ions in the layer direction of LDH particles. However, when considering application of LDH as a solid electrolyte separator to an alkaline secondary battery such as a zinc-air battery or a nickel-zinc battery, there is a problem that the LDH dense body has high resistance. Therefore, for practical use of LDH, it is desired to reduce the resistance by thinning. In this regard, the oriented LDH films disclosed in Patent Documents 1 and 2 and Non-Patent Document 1 are not sufficient in terms of denseness. Therefore, a highly densified LDH dense film is desired. In particular, when considering application of an LDH dense membrane as a solid electrolyte separator, hydroxide ions in the electrolyte must move through the LDH dense membrane, while substances other than hydroxide ions (especially in zinc secondary batteries) A high degree of denseness is desired such that Zn causing zinc dendrite growth and carbon dioxide causing alkali carbonate precipitation in a zinc-air battery are not transmitted as much as possible. In addition, such high denseness is not limited to the LDH dense film, and it is also desired that the dense film is made of other materials having hydroxide ion conductivity regardless of organic materials and inorganic materials. Nor.

  The present inventors have recently made contact with a Zn-containing aqueous solution on one surface of a hydroxide ion conductive dense membrane while contacting a Zn-free aqueous solution on the other surface, and evaluated the Zn transmission rate by Whether the oxide ion conductive dense membrane has a sufficiently high density suitable for predetermined applications such as battery separators (especially zinc secondary battery applications where zinc dendrite growth is a problem) is reliably and accurately evaluated. I learned that I can do it.

  Therefore, the object of the present invention is whether the hydroxide ion conductive dense membrane has a sufficiently high density suitable for a predetermined application such as a battery separator (especially a zinc secondary battery application where zinc dendrite growth is a problem). The object is to provide a method capable of reliably and accurately evaluating whether or not.

According to one aspect of the present invention, a method for evaluating the denseness of a hydroxide ion conducting dense membrane, comprising:
A first aqueous solution containing Zn is brought into contact with one surface of the hydroxide ion conductive dense membrane, and a second aqueous solution not containing Zn or water is brought into contact with the other surface of the dense membrane, Passing Zn through the dense film for a predetermined time;
Zn concentration C ₁ of the first aqueous solution before the start of Zn permeation, liquid volume V ₁ of the first aqueous solution before the start of Zn permeation, Zn concentration C ₂ of the second aqueous solution or water after the end of Zn permeation, the end of the Zn permeation Using the second aqueous solution or water volume V ₂ , Zn permeation time t, and film area S through which Zn permeates, (C ₂ × V ₂ ) / (C ₁ × V ₁ × t × S ) To calculate the Zn permeation ratio, and evaluating the denseness of the dense film based on the Zn permeation ratio,
A method is provided comprising:

It is a conceptual diagram which shows an example of Zn transmission measuring apparatus. It is a schematic cross section of the sample holder used for the measuring apparatus shown by FIG. 1A. It is a schematic diagram which shows a layered double hydroxide (LDH) plate-like particle. It is a SEM image of the surface of the porous substrate made from alumina produced in Example A1. It is a conceptual diagram which shows an example of He transmission measurement system. FIG. 4B is a schematic cross-sectional view of a sample holder used in the measurement system shown in FIG. 4A and its peripheral configuration. It is a graph which shows the relationship between He transmittance | permeability measured by Example A3 and A4, and Zn permeation | transmission ratio. It is the XRD profile obtained with respect to the crystal phase of a sample in Example B2. It is a SEM image which shows the surface microstructure of the film | membrane sample observed in Example B3. It is a SEM image of the grinding | polishing cross-section microstructure of the composite material sample observed in Example B3. It is a disassembled perspective view of the denseness discrimination | determination measurement system used in Example B5. It is a schematic cross section of the density discrimination | determination measurement system used in Example B5.

Evaluation method The present invention hydroxide ion conducting dense membrane is directed to a method of evaluating the compactness of the hydroxide ion conducting dense membrane. The hydroxide ion conductive dense membrane is preferably a layered double hydroxide dense membrane (LDH dense membrane), but is not limited thereto, and may be any dense membrane having hydroxide ion conductivity. It can be a film comprising an inorganic material and / or an organic material having hydroxide ion conductivity. In any case, it is desired that the hydroxide ion conductive dense membrane is a dense membrane that does not have water permeability. Although this dense membrane has hydroxide ion conductivity but does not have water permeability, it can function as a battery separator. As described above, when considering the application of LDH as a solid electrolyte separator for a battery, there was a problem that a bulk LDH dense body had high resistance, but the thickness was reduced by forming a dense film. Low resistance can be achieved. That is, the dense membrane can be a very useful material as a solid electrolyte separator applicable to various battery applications such as metal-air batteries (for example, zinc-air batteries) and other various zinc secondary batteries (for example, nickel-zinc batteries). However, when a defect having water permeability locally and / or accidentally exists in the dense film, the defect is filled with an appropriate repair agent (for example, epoxy resin) to repair the water impermeability. Such a repair agent need not necessarily have hydroxide ion conductivity.

The method of the present invention evaluates the presence or absence of denseness, particularly the presence or absence of a high level of denseness, in a dense film that should be essentially densely constructed as described above. For this purpose, the method of the present invention includes a step of allowing Zn to permeate the dense film for a predetermined time, and a step of calculating a Zn permeation ratio and evaluating the denseness of the dense film based on the Zn permeation ratio. . The permeation of Zn into the dense membrane is achieved by bringing the first aqueous solution containing Zn into contact with one surface of the hydroxide ion conductive dense membrane and the second aqueous solution not containing Zn on the other surface of the dense membrane. Or it is performed by making water contact. In addition, the Zn permeation ratio is the Zn concentration C ₁ of the first aqueous solution before the start of Zn permeation, the volume V ₁ of the first aqueous solution before the start of Zn permeation, the second aqueous solution after the completion of Zn permeation, or the Zn of water. (C ₂ × V ₂ ) / (C ₁ ) using the concentration C ₂ , the second aqueous solution or water volume V ₂ after the completion of Zn permeation, the Zn permeation time t, and the film area S through which Zn permeates. × is calculated by the equation of _{V 1} × t × S). Thus, by evaluating Zn permeability using a Zn-containing aqueous solution and a Zn-free solution, it is possible to evaluate the presence or absence of denseness at an extremely high level. It is possible to reliably and highly accurately evaluate high-density such that Zn that causes growth is not transmitted as much as possible (only a very small amount is transmitted). Then, by adopting an index called Zn transmission rate defined by the above-described formula, objective evaluation regarding denseness can be easily performed regardless of differences in various sample sizes and measurement conditions. This Zn transmission rate can be an effective index for judging the difficulty of precipitation of zinc dendrite. This is because when a hydroxide ion conductive dense membrane is used as a separator in a zinc secondary battery, even if Zn is contained in the negative electrode electrolyte on one side of the dense membrane (zinc negative electrode side), the other side This is because, in principle, it is considered that the growth of zinc dendrite in the positive electrode electrolyte is effectively suppressed unless Zn permeates the positive electrode electrolyte (which originally does not contain Zn). Thus, according to the method of the present invention, the hydroxide ion conductive dense membrane has a sufficiently high density suitable for a predetermined application such as a battery separator (especially a zinc secondary battery application where zinc dendrite growth is a problem). Whether or not it has can be evaluated reliably and with high accuracy.

In the method of the present invention, a first aqueous solution containing Zn is brought into contact with one surface of the hydroxide ion conductive dense membrane, and a second aqueous solution or water (without Zn) brought into contact with the other surface ( Hereinafter, Zn is permeated into the second aqueous solution. In contact with these aqueous solutions, the Zn concentration C ₁ of the first aqueous solution before the start of Zn permeation, the liquid volume V ₁ of the first aqueous solution before the start of Zn permeation, so that the Zn permeation ratio can be calculated in the subsequent steps. , A Zn concentration C ₂ of the second aqueous solution or water after completion of Zn permeation, a volume V ₂ of the second aqueous solution or water after termination of Zn permeation, and a membrane area S through which Zn permeates can be specified Is preferably carried out. An example of such a Zn transmission measuring device is shown in FIG. 1A. A measuring apparatus 10 shown in FIG. 1A is provided on a sample holder 12 for holding a dense film in the measuring apparatus, a first tank 14 provided on one side of the sample holder 12, and on the other side of the sample holder 12. And a second tank 16. A first aqueous solution 18 containing Zn is accommodated in the first tank 14 so as to come into contact with one surface of the dense film, while a second aqueous solution 20 not containing Zn is formed in the dense film in the second tank 16. The other surface is accommodated in a contactable manner. That is, the first aqueous solution 18 accommodated in the first tank 14 and the second aqueous solution 20 accommodated in the second tank 16 are completely partitioned by the dense film held in the sample holder 12. Therefore, it is possible to reliably and highly accurately evaluate at what ratio Zn contained in the first aqueous solution 18 permeates the second aqueous solution 20 through the dense film.

  As described above, the dense film is held in the measuring apparatus 10, particularly in the sample holder 12, prior to the permeation of Zn. An example of the sample holder 12 is shown in FIG. 1B. In the sample holder 12 shown in FIG. 1B, an adhesive 26 is disposed along the outer periphery of the dense film 22 (preferably provided in the form of a composite material formed on the porous substrate 24). It is configured to be attached to a jig 28 having an opening at the center. As shown in FIG. 1A, sealing members 30a and 30b such as packing are disposed on both sides of the jig 28, and are further sandwiched by flanges 32a and 32b from the outside of the sealing members 30a and 30b. . The flange 32 a is preferably integrated with the first tank 14. Similarly, the flange 32 b is preferably integrated with the second tank 16. When the dense film 22 is provided in the form of a composite material formed on the porous substrate 24, the dense film 22 side is disposed so as to be in contact with the first aqueous solution 18 containing Zn. , Which is preferable in that Zn permeability can be more reliably evaluated. The pair of flanges 32a and 32b are preferably fastened to each other by fastening means 34 such as screws so that no liquid leakage occurs. According to such a configuration, since assembly and disassembly can be easily performed, Zn permeability can be efficiently evaluated for a large number of dense films.

The first aqueous solution 18 is preferably an alkali metal hydroxide aqueous solution, and ZnO is preferably dissolved in the alkali metal hydroxide aqueous solution. The second aqueous solution 20 is preferably an alkali metal hydroxide aqueous solution in which ZnO is not dissolved, and more preferably the same type and the same as the first aqueous solution 18 except that ZnO is not dissolved. Concentration alkali metal hydroxide aqueous solution. A preferred alkali metal hydroxide is potassium hydroxide. Since an alkali metal hydroxide aqueous solution such as an aqueous potassium hydroxide solution is a typical electrolyte used in an alkaline battery such as a zinc secondary battery, by using an aqueous solution having a composition close to or equivalent to such an electrolyte, Zn permeability can be evaluated with high accuracy under conditions close to or equivalent to the mode of use as a battery separator (particularly a zinc secondary battery separator). In addition, it is preferable that a compound containing Al is dissolved in both the first aqueous solution and the second aqueous solution, which are alkali metal hydroxide aqueous solutions, and are dissolved at the same concentration in both the first and second aqueous solutions. More preferably. When an LDH dense film is brought into contact with an alkali metal hydroxide aqueous solution such as an aqueous potassium hydroxide solution, Al, which is a typical constituent element of LDH, may elute into the aqueous solution, leading to deterioration of the dense film. By adding a compound containing Al to the first and second aqueous solutions, such elution of Al and the resulting deterioration of the dense film can be prevented. The Al may be dissolved in the electrolytic solution in some form, and can typically be dissolved in the electrolytic solution in the form of a metal ion, a hydroxide and / or a hydroxy complex. For example, as ^the form in which Al is _{^{dissolved, Al 3+, Al (OH)}} 2+, Al (OH) 2 +, Al (OH) 3 0, Al (OH) 4 -, Al (OH) 5 2- etc. Can be mentioned. Preferable examples of the metal compound containing Al include aluminum hydroxide, γ alumina, α alumina, boehmite, diaspore, hydrotalcite, and any combination thereof, and more preferably aluminum hydroxide and / or γ alumina. And most preferably aluminum hydroxide. The compound containing Al is preferably added so that the Al concentration in the first aqueous solution and the second aqueous solution is 0.001 mol / L or more, more preferably 0.01 mol / L or more, and still more preferably 0.1 mol. / L or more, particularly preferably 1.0 mol / L or more, most preferably 2.0 mol / L or more, more than 3.0 mol / L, or 3.3 mol / L or more. The upper limit of the concentration of Al in the electrolytic solution is not particularly limited, and may reach the saturation solubility of the Al compound, but is, for example, 20 mol / L or less or 10 mol / L or less.

Next, the Zn permeation ratio is calculated to evaluate the denseness of the dense film. The Zn permeation ratio is the Zn concentration C ₁ of the first aqueous solution before the start of Zn permeation, the volume V ₁ of the first aqueous solution before the start of Zn permeation, the Zn concentration C of the second aqueous solution or water after the end of Zn permeation. ₂ , (C ₂ × V ₂ ) / (C ₁ × V), using the amount V ₂ of the second aqueous solution or water after completion of Zn permeation, the permeation time t of Zn, and the film area S through which Zn permeates. ₁ × t × S). The units of the parameters C ₁ , C ₂ , V ₁ , V ₂ , t and S are particularly limited as long as the units of the concentrations C ₁ and C ₂ are aligned and the units of the liquid amounts V ₁ and V ₂ are aligned. However, it is preferable that the unit of Zn transmission time t is h and the unit of film area S is m ² . The Zn concentration C ₁ of the first aqueous solution before Zn permeation is preferably in the range of 0.001 to ₁ mol / L, more preferably 0.01 to 1 mol / L, and still more preferably 0.05 to 0. 8 mol / L, particularly preferably 0.2 to 0.5 mol / L, most preferably 0.35 to 0.45 mol / L. The Zn permeation time is preferably 1 to 720 hours, more preferably 1 to 168 hours, still more preferably 6 to 72 hours, and particularly preferably 12 to 24 hours.

A dense membrane having a Zn permeation ratio of 10 m ⁻² · h ⁻¹ or less is certified as being suitable for the use of a hydroxide ion conductive separator for a secondary battery, and the certified dense membrane is optionally used for secondary battery water. It is preferable to use for the use of an oxide ion conductive separator. A dense membrane having a Zn permeation ratio of 10 m ⁻² · h ⁻¹ or less can very effectively suppress the permeation of Zn in the electrolytic solution, so that it is a hydroxide ion conductive separator for secondary batteries such as zinc secondary batteries. The growth of zinc dendrite can be suppressed when used in the above applications. The Zn permeation ratio of the dense film is preferably 10 m ⁻² · h ⁻¹ or less, more preferably 5.0 m ⁻² · h ⁻¹ or less, more preferably 4.0 m ⁻² · h ⁻¹ or less, more preferably It is 3.0 m ⁻² · h ⁻¹ or less, more preferably 1.0 m ⁻² · h ⁻¹ or less. Thus, the low Zn permeation ratio means that the permeation of Zn can be extremely effectively suppressed in the electrolytic solution. For this reason, it is considered in principle that the growth of zinc dendrites can be effectively effectively suppressed when used for applications of hydroxide ion conductive separators for secondary batteries such as zinc secondary batteries.

As hydroxide ion conducting dense membrane described above, the hydroxide ion-conducting dense membrane may be any dense film having a hydroxide ion conductivity, inorganic materials have, for example, hydroxide ion conductivity and / or It can be a film comprising an organic material. An inorganic material having hydroxide ion conductivity has a general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ^n- _{x / n} · mH ₂ O (wherein M ²⁺ is a divalent cation, M ³⁺ is a trivalent ^{cation, a n-n-valent} anion, n represents an integer of 1 or more, x is 0.1 to 0.4, m is represented by a is) 0 or more The layered double hydroxide is preferably included. That is, a preferred hydroxide ion conductive dense film is a layered double hydroxide dense film, that is, an LDH dense film (hereinafter referred to as an LDH film). The hydroxide ion conductive dense membrane is desirably a membrane that does not have water permeability.

LDH film of the general ^{_{formula: M 2+ 1-x M 3+}} x (OH) in _{2 A n- x / n · mH} 2 O ( ^{wherein, M 2+} is a divalent ^{cation, M 3+} is a trivalent cation A ⁿ⁻ is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more), a layered double hydroxide (LDH) ), Preferably consisting mainly of such LDH. In the above general formula, M ²⁺ may be any divalent cation, and preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ may be any trivalent cation, but preferred examples include Al ³⁺ or Cr ³⁺ , and more preferred is Al ³⁺ . A ^n- may be any anion, preferred examples OH ^- and _CO ^{3 2-} and the like. Accordingly, the general formula is an ^{Mg 2+} at least ^{M 2+,} include ^{Al 3+} in ^{M 3+,} to ^{A n-OH -} and / or _CO preferably contains ^{3 2-.} n is an integer of 1 or more, preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is a real number or an integer of 0 or more, typically more than 0 or 1 or more.

  The layered double hydroxide contained in the LDH film is composed of an assembly of a plurality of plate-like particles (that is, LDH plate-like particles), and the plate-like particles have a plate surface whose surface (base) It is preferably oriented in a direction that intersects the surface of the material substantially perpendicularly or obliquely. That is, the LDH crystal is known to have the form of a plate-like particle having a layered structure as shown in FIG. 3, but the substantially vertical or oblique orientation is a very advantageous characteristic for the LDH film. . This is because, in an oriented LDH film, the hydroxide ion conductivity in the direction in which the LDH plate-like particles are oriented (that is, the direction parallel to the LDH layer) is much higher than the conductivity in the direction perpendicular thereto. This is because of the conductivity anisotropy. In fact, the present inventors have found that in an LDH oriented bulk body, the conductivity (S / cm) in the orientation direction is an order of magnitude higher than the conductivity (S / cm) in the direction perpendicular to the orientation direction. It has gained. That is, the substantially vertical or oblique alignment in the LDH film maximizes the conductivity anisotropy that the LDH alignment body can have in the layer thickness direction (that is, the direction perpendicular to the surface of the LDH film or the porous substrate). As a result, the conductivity in the layer thickness direction can be maximized or significantly increased. In addition, since the LDH film has a layer form, lower resistance than the bulk form LDH can be realized. An LDH film having such an orientation easily conducts hydroxide ions in the layer thickness direction. In addition, since it is densified, it is extremely suitable for use in functional membranes such as battery separators (eg, hydroxide ion conductive separators for zinc-air batteries) where high conductivity in the layer thickness direction and denseness are desired. Suitable.

  Particularly preferably, the LDH plate-like particles are highly oriented in a substantially vertical direction in the LDH film. This high degree of orientation is confirmed by the fact that when the surface of the LDH film is measured by the X-ray diffraction method, the peak of the (003) plane is not substantially detected or smaller than the peak of the (012) plane. (However, when a porous substrate in which a diffraction peak is observed at the same position as the peak due to the (012) plane is used, the peak of the (012) plane due to the LDH plate-like particle is used. This is not the case). This characteristic peak characteristic indicates that the LDH plate-like particles constituting the LDH film are oriented in a substantially vertical direction (that is, a vertical direction or an oblique direction similar thereto, preferably a vertical direction) with respect to the LDH film. That is, the peak on the (003) plane is known as the strongest peak observed when X-ray diffraction is performed on non-oriented LDH powder. In an oriented LDH film, LDH plate-like particles are formed on the LDH film. On the other hand, the (003) plane peak is not substantially detected or is smaller than the (012) plane peak because of being oriented in a substantially vertical direction. This is because the c-axis direction (00l) plane (l is 3 and 6) to which the (003) plane belongs is a plane parallel to the layered structure of the LDH plate-like particle. On the other hand, when oriented in a substantially vertical direction, the LDH layered structure also faces in the substantially vertical direction. As a result, when the surface of the LDH film is measured by X-ray diffraction, the (00l) plane (l is 3 and 6). This is because the peak of) does not appear or becomes difficult to appear. In particular, the peak of the (003) plane tends to be stronger than the peak of the (006) plane when it exists, so it is easier to evaluate the presence / absence of orientation in the substantially vertical direction than the peak of the (006) plane. I can say that. Therefore, it is preferable that the oriented LDH film has a (003) plane substantially not detected or smaller than the (012) plane peak because it suggests a high degree of vertical orientation. I can say that. In this regard, the LDH alignment films disclosed in Patent Documents 1 and 2 and Non-Patent Document 1 are those in which the peak of the (003) plane is detected strongly, and are considered to be inferior in alignment in the substantially vertical direction. Moreover, it seems that it does not have high density.

  The hydroxide ion conductive dense membrane (preferably LDH membrane) preferably has a thickness of 100 μm or less, more preferably 75 μm or less, further preferably 50 μm or less, particularly preferably 25 μm or less, and most preferably 5 μm or less. . Such a thin film can reduce the resistance of the dense film. When the thickness is as described above, a desired low resistance suitable for practical use in battery applications and the like can be realized. The lower limit of the thickness of the dense film is not particularly limited because it varies depending on the application, but in order to ensure a certain degree of rigidity desired as a functional film such as a separator, the thickness is preferably 1 μm or more, more preferably Is 2 μm or more.

  The hydroxide ion conductive dense film (preferably LDH film) may have a non-flat surface structure on at least one side. This non-planar surface structure is rich in gaps and / or undulations, resulting in a very high surface area structure. Therefore, when it is brought into contact with the electrolytic solution to be used as a separator, the area of the interface with the electrolytic solution increases, and as a result, the interface resistance can be lowered. An LDH separator having a low interface resistance with an electrolytic solution can be provided by providing a dense layer structure having hydroxide ion conductivity but not water permeability while having such a surface structure. It becomes possible. The non-flat surface structure preferably includes acicular particles protruding in a direction away from the dense film (typically in a direction substantially perpendicular to the dense film). The surface area can be significantly increased due to the presence of the acicular particles, and thereby the interface resistance when brought into contact with the electrolytic solution can be significantly more effectively reduced. The cross-sectional diameter of the acicular particles is preferably 0.01 to 0.5 μm, more preferably 0.01 to 0.3 μm. The height of the acicular particles is preferably 0.5 to 3.0 μm, more preferably 1 to 3 μm. In the present specification, the height of the acicular particles means the height of a portion protruding from the surface of the dense film as a reference. It is also preferred that the non-flat surface structure comprises open pore coarse particles rich in voids. The presence of the open pore coarse particles can significantly increase the surface area, thereby more effectively reducing the interfacial resistance when in contact with the electrolyte. Particularly preferable open pore coarse particles are aggregated particles formed by aggregating a plurality of needle-like or plate-like particles so as to be entangled with each other to form a plurality of voids, and the aggregated particles in this form are marimo (diatomaceous) particles. It is particularly excellent in the effect of increasing the surface area. The open pore coarse particles preferably have a diameter of 0.5 to 30 μm in the direction parallel to the dense membrane, and more preferably 0.5 to 20 μm. The height of the open pore coarse particles is preferably 0.5 to 30 μm, more preferably 1 to 30 μm. In the present specification, the height of the open pore coarse particles means the height of a portion protruding from the surface of the dense membrane. The non-flat surface structure preferably includes both acicular particles and open pore coarse particles.

The dense composite material film (preferably LDH film) is preferably provided on at least one surface of the porous substrate. That is, according to a preferred embodiment of the present invention, the dense film is prepared in the form of a composite material provided on at least one surface of the porous substrate. Here, the surface of the porous substrate mainly refers to the outermost surface of the plate surface when the rough shape of the porous substrate is viewed macroscopically as a plate, but is microscopically seen in the porous substrate. Needless to say, the surface of the hole existing in the vicinity of the outermost surface of the plate surface can be included.

  The porous substrate is preferably capable of forming an LDH film on its surface, and the material and porous structure are not particularly limited. Typically, an LDH film is formed on the surface of a porous substrate, but an LDH film is formed on a nonporous substrate, and then the nonporous substrate is made porous by various known methods. Also good. In any case, it is preferable that the porous base material has a porous structure having water permeability in that the electrolyte solution can reach the LDH film when incorporated into a battery as a battery separator.

  The porous substrate is preferably composed of at least one selected from the group consisting of ceramic materials, metal materials, and polymer materials. More preferably, the porous substrate is made of a ceramic material. In this case, preferable examples of the ceramic material include alumina, zirconia, titania, magnesia, spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, aluminum nitride, silicon nitride, and any combination thereof. More preferred are alumina, zirconia, titania, and any combination thereof, and particularly preferred are alumina, zirconia (eg, yttria stabilized zirconia (YSZ)), and combinations thereof. When these porous ceramics are used, it is easy to form an LDH film having excellent denseness. Preferable examples of the metal material include aluminum and zinc. Preferred examples of the polymer material include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, and any combination thereof. Any of the various preferred materials described above has alkali resistance as resistance to the electrolyte of the battery.

  The porous substrate preferably has an average pore diameter of 0.001 to 1.5 μm, more preferably 0.001 to 1.25 μm, still more preferably 0.001 to 1.0 μm, and particularly preferably 0.001. It is -0.75 micrometer, Most preferably, it is 0.001-0.5 micrometer. By setting it within these ranges, it is possible to form an LDH film that is so dense that it does not have water permeability (preferably water permeability and air permeability) while ensuring the desired water permeability in the porous substrate. In the present specification, “not having water permeability” means that a measurement object (that is, LDH) is measured when water permeability is evaluated by a “denseness determination test” employed in B5 described later or a method or configuration according thereto. It means that water that contacts one side of the membrane and / or porous substrate does not permeate the other side. In the present invention, the average pore diameter can be measured by measuring the longest distance of the pores based on the electron microscope image of the surface of the porous substrate. The magnification of the electron microscope image used for this measurement is 20000 times or more, and all obtained pore diameters are arranged in the order of size, and the upper 15 points and the lower 15 points from the average value. The average pore size can be obtained by calculating the average value of minutes. For the length measurement, a length measurement function of an electron microscope software, image analysis software (for example, Photoshop, manufactured by Adobe) or the like can be used.

  The surface of the porous substrate preferably has a porosity of 10 to 60%, more preferably 15 to 55%, and still more preferably 20 to 50%. By setting it within these ranges, it is possible to form an LDH film that is so dense that it does not have water permeability (preferably water permeability and air permeability) while ensuring the desired water permeability in the porous substrate. Here, the porosity of the surface of the porous substrate is adopted because it is easy to measure the porosity using the image processing described below, and the porosity of the surface of the porous substrate. This is because it can be said that it generally represents the porosity inside the porous substrate. That is, if the surface of the porous substrate is dense, the inside of the porous substrate can be said to be dense as well. In the present invention, the porosity of the surface of the porous substrate can be measured as follows by a technique using image processing. That is, 1) an electron microscope image (a magnification of 10,000 times or more) of the surface of the porous substrate is acquired, and 2) a gray scale electron microscope image is read using image analysis software such as Photoshop (manufactured by Adobe). ) Create a black-and-white binary image by the procedure of [Image] → [Tone Correction] → [2 Gradation], and 4) Porosity (the value obtained by dividing the number of pixels occupied by the black part by the total number of pixels in the image) %). The porosity measurement by this image processing is preferably performed for a 6 μm × 6 μm region on the surface of the porous substrate. In order to obtain a more objective index, three arbitrarily selected regions are used. It is more preferable to employ the average value of the obtained porosity.

Manufacturing method LDH film and LDH-containing composite material: (a) A porous substrate is prepared, and (b) A starting material capable of giving a starting point for crystal growth of LDH is uniformly attached to this porous substrate, if desired. (C) The porous substrate can be preferably manufactured by subjecting the porous substrate to hydrothermal treatment to form an LDH film.

(A) Preparation of porous substrate The porous substrate is as described above, and is preferably composed of at least one selected from the group consisting of ceramic materials, metal materials, and polymer materials. More preferably, the porous substrate is made of a ceramic material. In this case, preferable examples of the ceramic material include alumina, zirconia, titania, magnesia, spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, aluminum nitride, silicon nitride, and any combination thereof. More preferred are alumina, zirconia, titania, and any combination thereof, and particularly preferred are alumina, zirconia (eg, yttria stabilized zirconia (YSZ)), and combinations thereof. When these porous ceramics are used, the density of the LDH film tends to be improved. When using a porous substrate made of a ceramic material, it is preferable to subject the porous substrate to ultrasonic cleaning, cleaning with ion exchange water, and the like.

  As described above, the porous substrate is more preferably composed of a ceramic material. The porous substrate made of a ceramic material may be a commercially available product or may be prepared according to a known technique, and is not particularly limited. For example, ceramic powder (for example, zirconia powder, boehmite powder, titania powder, etc.), methylcellulose, and ion-exchanged water are kneaded at a desired blending ratio, the obtained kneaded product is subjected to extrusion molding, and the resulting molded body is obtained. After drying at 70 to 200 ° C. for 10 to 40 hours, a porous substrate made of a ceramic material can be produced by firing at 900 to 1300 ° C. for 1 to 5 hours. The blending ratio of methylcellulose is preferably 1 to 20 parts by weight with respect to 100 parts by weight of the ceramic powder. Further, the blending ratio of the ion exchange water is preferably 10 to 100 parts by weight with respect to 100 parts by weight of the ceramic powder.

(B) Attachment of starting material If desired, a starting material that can provide a starting point for crystal growth of LDH may be uniformly attached to the porous substrate. After the starting material is uniformly attached to the surface of the porous substrate in this way, the subsequent step (c) is performed, so that a highly densified LDH film can be uniformly formed on the surface of the porous substrate. It can be formed uniformly. Preferable examples of such an origin include a chemical species that provides an anion that can enter between the layers of LDH, a chemical species that provides a cation that can be a constituent element of LDH, or LDH.

(I) Chemical species that provide anions The starting point of crystal growth of LDH can be a chemical species that provides anions that can enter between layers of LDH. Examples of such anions include CO ₃ ²⁻ , OH ⁻ , SO ₃ ⁻ , SO ₃ ²⁻ , SO ₄ ²⁻ , NO ₃ ⁻ , Cl ⁻ , Br ⁻ , and any combination thereof. It is done. Therefore, the starting material that can provide such a starting point may be uniformly attached to the surface of the porous substrate by an appropriate method according to the type of the starting material. By applying a chemical species that gives an anion to the surface, metal cations such as Mg ²⁺ and Al ³⁺ can be adsorbed on the surface of the porous substrate to generate LDH nuclei. Therefore, by performing the subsequent step (c), a highly densified LDH film can be uniformly formed on the surface of the porous substrate without unevenness.

According to a preferred embodiment of the present invention, the starting material can be attached by attaching a polymer to the surface of the porous substrate and then introducing a chemical species that gives an anion to the polymer. In this embodiment, the anion is preferably SO ₃ ⁻ , SO ₃ ²⁻ and / or SO ₄ ²⁻ , and introduction of a chemical species giving such an anion into the polymer is performed by sulfonation treatment. Is preferred. Polymers that can be used are anionizable (especially sulfonated) polymers, examples of such polymers include polystyrene, polyethersulfone, polypropylene, epoxy resins, polyphenylene sulfide, and any combination thereof. . In particular, the aromatic polymer is preferable in that it is easily anionized (particularly sulfonated). Examples of such aromatic polymer include polystyrene, polyethersulfone, epoxy resin, polyphenylene sulfide, and any of them. Combinations are mentioned. The most preferred polymer is polystyrene. The adhesion of the polymer to the porous substrate is performed by using a solution in which the polymer is dissolved (hereinafter referred to as a polymer solution) as the surface of the porous substrate (preferably, the outermost surface of the plate-like outline of the porous substrate). ) Is preferably applied by coating. The polymer solution can be easily prepared, for example, by dissolving a polymer solid (for example, a polystyrene substrate) in an organic solvent (for example, a xylene solution). It is preferable to prevent the polymer solution from penetrating into the porous substrate because it is easy to achieve uniform coating. In this respect, the polymer solution is preferably attached or applied by spin coating because it can be applied uniformly. The spin coating conditions are not particularly limited. For example, the spin coating may be performed at a rotational speed of 1000 to 10000 rpm for about 60 to 300 seconds including dripping and drying. On the other hand, the sulfonation treatment may be performed by immersing the porous substrate to which the polymer is attached in a sulfonateable acid such as sulfuric acid (for example, concentrated sulfuric acid), fuming sulfuric acid, chlorosulfonic acid, and sulfuric anhydride. Alternatively, the technology may be used. The immersion in the sulfonateable acid may be performed at room temperature or high temperature (for example, 50 to 150 ° C.), and the immersion time is not particularly limited, but is, for example, 1 to 14 days.

According to another preferred embodiment of the present invention, the starting material can be attached by treating the surface of the porous substrate with a surfactant containing a chemical species that gives an anion as a hydrophilic group. In this case, the anion is preferably SO ₃ ⁻ , SO ₃ ²⁻ and / or SO ₄ ²⁻ . A typical example of such a surfactant is an anionic surfactant. Preferred examples of the anionic surfactant include a sulfonic acid type anionic surfactant, a sulfate type anionic surfactant, and any combination thereof. Examples of the sulfonic acid type anionic surfactant include naphthalene sulfonic acid Na formalin condensate, polyoxyethylene sulfosuccinic acid alkyl 2Na, polystyrene sulfonic acid Na, dioctyl sulfosuccinic acid Na, polyoxyethylene lauryl ether sulfate triethanolamine. It is done. Examples of the sulfate ester type anionic surfactant include polyoxyethylene lauryl ether sulfate Na. The treatment of the porous substrate with the surfactant is not particularly limited as long as it is a technique capable of attaching the surfactant to the surface of the porous substrate, and a solution containing the surfactant is applied to the porous substrate. What is necessary is just to apply | coat or immerse a porous base material in the solution containing surfactant. The porous substrate may be immersed in the solution containing the surfactant while stirring the solution at room temperature or high temperature (for example, 40 to 80 ° C.), and the immersion time is not particularly limited, but for example, 1 to 7 days. is there.

(Ii) Chemical species that provide cations The starting point of LDH crystal growth can be a chemical species that provides cations that can be a component of the layered double hydroxide. A preferred example of such a cation is Al ³⁺ . In this case, the starting material is preferably at least one aluminum compound selected from the group consisting of aluminum oxides, hydroxides, oxyhydroxides, and hydroxy complexes. Therefore, the starting material that can provide such a starting point may be uniformly attached to the surface of the porous member by an appropriate method according to the type of the starting material. By imparting a chemical species that gives a cation to the surface, an anion that can enter between the layers of LDH can be adsorbed on the surface of the porous substrate to generate LDH nuclei. Therefore, by performing the subsequent step (c), a highly densified LDH film can be uniformly formed on the surface of the porous substrate without unevenness.

According to a preferred aspect of the present invention, the starting material can be attached by applying a sol containing an aluminum compound to the porous member. In this case, examples of preferred aluminum compounds include boehmite (AlOOH), aluminum hydroxide (Al (OH) ₃ ), and amorphous alumina, with boehmite being most preferred. The application of the sol containing the aluminum compound is preferably performed by spin coating because it can be applied uniformly. The spin coating conditions are not particularly limited. For example, the spin coating may be performed at a rotational speed of 1000 to 10000 rpm for about 60 to 300 seconds including dripping and drying.

According to another preferred embodiment of the present invention, the starting material is adhered by subjecting the porous substrate to hydrothermal treatment in an aqueous solution containing at least aluminum to form an aluminum compound on the surface of the porous substrate. be able to. The aluminum compound formed on the surface of the porous substrate is preferably Al (OH) ₃ . In particular, LDH films on porous substrates (especially ceramic porous substrates) tend to produce crystalline and / or amorphous Al (OH) _{3 in the} initial stage of growth. Can grow. Therefore, after the Al (OH) ₃ is uniformly attached to the surface of the porous substrate by hydrothermal treatment in advance, the step (c) that also involves hydrothermal treatment is performed, The LDH film can be uniformly formed without unevenness. In this embodiment, the step (b) and the subsequent step (c) may be performed continuously in the same sealed container, or the step (b) and the subsequent step (c) are performed separately in this order. May be.

When the step (b) and the step (c) are continuously performed in the same sealed container, the raw material aqueous solution (that is, the aqueous solution containing the constituent elements of LDH) used in the step (c) described later is used as it is in the step (b). Can be used. Even in this case, the hydrothermal treatment in the step (b) is compared with 50 to 70 ° C. in an acidic or neutral pH range (preferably pH 5.5 to 7.0) in an airtight container (preferably an autoclave). By performing in a low temperature region, not LDH but Al
(OH) ₃ nucleation can be promoted. In addition, after the nucleation of Al (OH) ₃ , the pH of the raw material aqueous solution rises due to the hydrolysis of urea by holding or raising the temperature at the nucleation temperature, and therefore a pH range suitable for LDH growth. It is possible to smoothly shift to step (c) at (preferably more than pH 7.0).

On the other hand, when the step (b) and the step (c) are separately performed in this order, it is preferable to use different raw material aqueous solutions in the step (b) and the step (c). For example, in step (b), it is preferable to nucleate Al (OH) ₃ using a raw material aqueous solution mainly containing an Al source (preferably not containing other metal elements). In this case, the hydrothermal treatment in the step (b) may be performed at 50 to 120 ° C. in a closed container (preferably an autoclave) different from the step (c). Preferable examples of the raw material aqueous solution mainly containing an Al source include an aqueous solution containing aluminum nitrate and urea and not containing a magnesium compound (for example, magnesium nitrate). By using a raw material aqueous solution not containing Mg, precipitation of LDH can be avoided and nucleation of Al (OH) ₃ can be promoted.

According to still another preferred embodiment of the present invention, the starting material is adhered by depositing aluminum on the surface of the porous substrate and then converting the aluminum into an aluminum compound by hydrothermal treatment in an aqueous solution. Can do. This aluminum compound is preferably Al
(OH) ₃ . In particular, by converting to Al (OH) ₃ , the growth of LDH can be promoted using this as a nucleus. Therefore, after the Al (OH) ₃ is uniformly formed on the surface of the porous base material by hydrothermal treatment, the same process (c) accompanied by hydrothermal treatment is carried out. A densified LDH film can be uniformly formed without unevenness. Aluminum may be deposited by physical vapor deposition or chemical vapor deposition, but physical vapor deposition such as vacuum vapor deposition is preferred. Moreover, the aqueous solution used for the hydrothermal treatment for aluminum conversion should just be a composition which can react with Al already provided by vapor deposition and can produce | generate Al (OH) _3, and is not specifically limited.

(Iii) LDH as a starting point
The starting point for crystal growth can be LDH. In this case, the growth of LDH can be promoted starting from the nucleus of LDH. Therefore, after the LDH nuclei are uniformly attached to the surface of the porous base material, the subsequent step (c) is performed to unevenly disperse the highly densified LDH film on the surface of the porous base material. And can be formed uniformly.

  According to a preferred aspect of the present invention, the starting material can be attached by applying a sol containing LDH to the surface of the porous member. The sol containing LDH may be prepared by dispersing LDH in a solvent such as water, and is not particularly limited. In this case, the application is preferably performed by spin coating. Spin coating is preferred because it can be applied very uniformly. The spin coating conditions are not particularly limited. For example, the spin coating may be performed at a rotational speed of 1000 to 10000 rpm for about 60 to 300 seconds including dripping and drying.

  According to another preferred embodiment of the present invention, the deposition of the starting material is performed by depositing aluminum (deposited) in an aqueous solution containing a constituent element of LDH other than aluminum after depositing aluminum on the surface of the porous substrate. It can be performed by converting to LDH by hydrothermal treatment. Aluminum may be deposited by physical vapor deposition or chemical vapor deposition, but physical vapor deposition such as vacuum vapor deposition is preferred. Moreover, the raw material aqueous solution used for the hydrothermal treatment for the conversion of aluminum may be performed using an aqueous solution containing a component other than Al already provided by vapor deposition. A preferable example of such a raw material aqueous solution is a raw material aqueous solution mainly containing a Mg source, and more preferably, an aqueous solution containing magnesium nitrate and urea and not containing an aluminum compound (aluminum nitrate). By including the Mg source, the nuclei of LDH can be formed together with Al already provided by vapor deposition.

(C) Hydrothermal treatment A hydrothermal treatment is performed on a porous substrate (a starting material can be attached if desired) in a raw material aqueous solution containing a constituent element of LDH to form an LDH film on the surface of the porous substrate. A preferable raw material aqueous solution contains magnesium ions (Mg ²⁺ ) and aluminum ions (Al ³⁺ ) at a predetermined total concentration, and contains urea. Due to the presence of urea, ammonia is generated in the solution by utilizing hydrolysis of urea, so that the pH value rises (for example, more than pH 7.0, preferably more than 7.0 and less than 8.5) and coexists. LDH can be obtained when metal ions form hydroxides. Further, since carbon dioxide is generated in the hydrolysis, LDH in which the anion is carbonate ion type can be obtained. The total concentration (Mg ²⁺ + Al ³⁺ ) of magnesium ions and aluminum ions contained in the raw material aqueous solution is preferably 0.20 to 0.40 mol / L, more preferably 0.22 to 0.38 mol / L, still more preferably 0.24 to 0.36 mol / L, particularly preferably 0.26 to 0.34 mol / L. When the concentration is within such a range, nucleation and crystal growth can proceed in a balanced manner, and an LDH film excellent not only in orientation but also in denseness can be obtained. That is, when the total concentration of magnesium ions and aluminum ions is low, crystal growth becomes dominant compared to nucleation, and the number of particles decreases and particle size increases. It is considered that the generation becomes dominant, the number of particles increases, and the particle size decreases.

Preferably, magnesium nitrate and aluminum nitrate are dissolved in the raw material aqueous solution, so that the raw material aqueous solution contains nitrate ions in addition to magnesium ions and aluminum ions. In this case, the molar ratio (urea / NO ₃ ⁻ ) of urea to nitrate ions (NO ₃ ⁻ ) in the raw material aqueous solution is preferably 2 to 6, and more preferably 4 to 5.

  The porous substrate may be immersed in the raw material aqueous solution in a desired direction (for example, horizontally or vertically). When the porous substrate is held horizontally, the porous substrate may be suspended, floated, or disposed so as to be in contact with the bottom of the container. For example, the porous substrate is suspended from the bottom of the container in the raw material aqueous solution. The material may be fixed. When the porous substrate is held vertically, a jig that can set the porous substrate vertically on the bottom of the container may be placed. In any case, LDH is substantially perpendicular to or close to the porous substrate (that is, the LDH plate-like particles have their plate surfaces intersecting the surface (substrate surface) of the porous substrate substantially perpendicularly or obliquely. It is preferable to adopt a configuration or arrangement in which growth is performed in such a direction.

In the raw material aqueous solution, the porous substrate is subjected to hydrothermal treatment to form an LDH film on the surface of the porous substrate. This hydrothermal treatment is preferably carried out in a sealed container (preferably an autoclave) at 60 to 150 ° C., more preferably 65 to 120 ° C., further preferably 65 to 100 ° C., particularly preferably 70 to 90 ° C. The upper limit temperature of the hydrothermal treatment may be selected so that the porous substrate (for example, the polymer substrate) is not deformed by heat. The rate of temperature increase during the hydrothermal treatment is not particularly limited and may be, for example, 10 to 200 ° C./h, preferably 100 to 200 ° C./h, more preferably 100 to 150 ° C./h. The hydrothermal treatment time may be appropriately determined according to the target density and thickness of the LDH film.

  After the hydrothermal treatment, the porous substrate is preferably taken out from the sealed container and washed with ion exchange water.

  The LDH film produced as described above is one in which LDH plate-like particles are highly densified and oriented in a substantially vertical direction that is advantageous for conduction. That is, the LDH film typically does not have water permeability (desirably water permeability and air permeability) due to high density. In addition, the LDH constituting the LDH film is composed of an aggregate of a plurality of plate-like particles, and the plurality of plate-like particles cross their surfaces substantially perpendicularly or obliquely with the surface of the porous substrate. Typically oriented in the direction. Accordingly, when an LDH film having sufficient gas tightness and a dense LDH film is used for a battery such as a zinc-air battery, an improvement in power generation performance can be expected, and a secondary battery for a zinc-air battery using an electrolyte that has not been conventionally applicable It is expected to be applied to new separators such as zinc dendrite progress barriers and carbon dioxide intrusion separators, which have become major barriers to chemical conversion. Similarly, it is expected to be applied to a nickel-zinc battery in which the progress of zinc dendrite is a major barrier to practical use.

  By the way, the LDH film obtained by the above production method can be formed on both surfaces of the porous substrate. For this reason, in order to make the LDH film suitable for use as a separator, the LDH film on one side of the porous substrate is mechanically scraped after film formation, or the LDH film is formed on one side during film formation. It is desirable to take measures that prevent film formation.

  The present invention is more specifically described by the following examples.

Example A1
In this example, samples A1 to A10 were produced as follows as LDH-containing composite material samples in which a layered double hydroxide (LDH) film was formed on a porous substrate.

(1) Production of porous substrate Boehmite (manufactured by Sasol, DISPAL 18N4-80), methylcellulose, and ion-exchanged water are mixed at a weight ratio of 10: 1: (boehmite) :( methylcellulose) :( ion-exchanged water). After weighing so as to be 5, kneaded. The obtained kneaded product was subjected to extrusion molding using a hand press and molded into a size of 2.5 cm × 10 cm × thickness 0.5 cm. The obtained molded body was dried at 80 ° C. for 12 hours and then calcined at 1150 ° C. for 3 hours to obtain an alumina porous substrate.

  With respect to the obtained porous substrate, the porosity on the surface of the porous substrate was measured by a technique using image processing, and it was 24.6%. The porosity is measured by 1) observing the surface microstructure using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV, and an electron microscope on the surface of the porous substrate ( SEM) image (magnification of 10,000 times or more) is obtained, 2) a grayscale SEM image is read using image analysis software such as Photoshop (manufactured by Adobe), etc. 3) [Image] → [Tone Correction] → [2 A monochrome binary image was created by the procedure of [gradation], and 4) the porosity (%) was obtained by dividing the number of pixels occupied by the black portion by the total number of pixels in the image. This porosity measurement was performed on a 6 μm × 6 μm region on the surface of the porous substrate. FIG. 3 shows an SEM image of the porous substrate surface.

  Moreover, it was about 0.1 micrometer when the average hole diameter of the porous base material was measured. In the present invention, the average pore diameter was measured by measuring the longest distance of the pores based on an electron microscope (SEM) image of the surface of the porous substrate. The magnification of the electron microscope (SEM) image used for this measurement is 20000 times, and all the obtained pore diameters are arranged in order of size, and the top 15 points and the bottom 15 points from the average value, and 30 points per visual field in total. The average value for two visual fields was calculated to obtain the average pore diameter. For length measurement, the length measurement function of SEM software was used.

(2) Cleaning of porous substrate The obtained porous substrate was ultrasonically cleaned in acetone for 5 minutes, ultrasonically cleaned in ethanol for 2 minutes, and then ultrasonically cleaned in ion-exchanged water for 1 minute.

(3) Polystyrene spin coating and sulfonation For the samples A1 to A6, polystyrene spin coating and sulfonation were performed on the porous substrate by the following procedure. That is, 0.6 g of a polystyrene substrate was dissolved in 10 ml of a xylene solution to prepare a spin coating solution having a polystyrene concentration of 0.06 g / ml. 0.1 ml of the obtained spin coating solution was dropped onto the porous substrate and applied by spin coating at a rotation speed of 8000 rpm. This spin coating was performed for 200 seconds including dripping and drying. The porous substrate coated with the spin coating solution was immersed in 95% sulfuric acid at 25 ° C. for 4 days for sulfonation.

(4) As the manufacturing raw material of the raw aqueous solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate _{(Al (NO 3) 3 ·} 9H ₂ O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate so that the cation ratio (Mg ²⁺ / Al ³⁺ ) is 2 and the total metal ion molar concentration (Mg ²⁺ + Al ³⁺ ) is 0.320 mol / L. In a beaker, ion exchange water was added to make a total volume of 75 ml. After stirring the obtained solution, urea weighed at a ratio of urea / NO ₃ ⁻ = 4 was added to the solution, and further stirred to obtain a raw material aqueous solution.

(5) Film formation by hydrothermal treatment A Teflon (registered trademark) sealed container (with an internal volume of 100 ml, the outside is a stainless steel jacket) and the raw material aqueous solution prepared in (4) above and the porous substrate sulfonated in (3) above (Samples A1 to A6) or the porous substrate (samples A7 to A10) washed in (2) above were encapsulated together. At this time, the base material was fixed by being floated from the bottom of a Teflon (registered trademark) sealed container, and placed horizontally so that the solution was in contact with both surfaces of the base material. Then, the layered double hydroxide alignment film was formed on the substrate surface by performing hydrothermal treatment at a hydrothermal temperature of 70 to 75 ° C. for 168 to 504 hours. At this time, ten kinds of alignment films having various denseness were produced by appropriately changing the conditions of the hydrothermal treatment. After the elapse of a predetermined time, the substrate is taken out from the sealed container, washed with ion-exchanged water, dried at 70 ° C. for 10 hours, and a dense layer of layered double hydroxide (hereinafter referred to as LDH) (hereinafter referred to as a membrane sample). ) Was obtained on a substrate. The thickness of the obtained film sample was about 1.0 to 2.0 μm. Thus, samples A1 to A10 were obtained as LDH-containing composite material samples (hereinafter referred to as composite material samples). In addition, although the LDH film was formed on both surfaces of the porous substrate, the LDH film on one surface of the porous substrate was mechanically scraped to give the composite material a form as a separator.

Example A2 : Identification of a film sample Using an X-ray diffractometer (RINT TTR III manufactured by Rigaku Corporation), the crystal phase of the film sample was measured under the measurement conditions of voltage: 50 kV, current value: 300 mA, measurement range: 10 to 70 °. To obtain an XRD profile. About the obtained XRD profile, JCPDS card NO. Identification was performed using a diffraction peak of a layered double hydroxide (hydrotalcite compound) described in 35-0964. As a result, it was confirmed that all of the film samples A1 to A10 were layered double hydroxides (LDH, hydrotalcite compounds).

Example A3 : He permeation measurement A He permeation test was performed as follows to evaluate the denseness of the membrane samples A1 to A10 from the viewpoint of He permeability. First, the He transmittance measurement system 40 shown in FIGS. 4A and 4B was constructed. In the He permeability measurement system 40, He gas from a gas cylinder filled with He gas is supplied to a sample holder 46 via a pressure gauge 42 and a flow meter 44 (digital flow meter), and the denseness held in the sample holder 46 is measured. The membrane 48 was configured to be transmitted through one surface from the other surface and discharged.

  The sample holder 46 has a structure including a gas supply port 46a, a sealed space 46b, and a gas discharge port 46c, and was assembled as follows. First, the adhesive 52 was applied along the outer periphery of the dense film 48 and attached to a jig 54 (made of ABS resin) having an opening at the center. Sealing members 56a and 56b are provided with packings made of butyl rubber at the upper and lower ends of the jig 54, and support members 58a and 58b (made of PTFE) provided with openings made of flanges from outside the sealing members 56a and 56b. ). Thus, the sealed space 46b was defined by the dense film 48, the jig 54, the sealing member 56a, and the support member 58a. The dense film 48 is in the form of a composite material formed on the porous substrate 50, but is arranged so that the dense film 48 side faces the gas supply port 46a. The support members 58a and 58b were firmly fastened to each other by the fastening means 60 using screws so that He gas does not leak from portions other than the gas discharge port 46c. A gas supply pipe 64 was connected via a joint 62 to the gas supply port 46 a of the sample holder 46 thus assembled.

Next, He gas was supplied to the He permeability measurement system 40 through the gas supply pipe 64 and permeated through the dense film 48 held in the sample holder 46. At this time, the gas supply pressure and flow rate were monitored by the pressure gauge 42 and the flow meter 44. After permeating He gas for 1 to 30 minutes, the He permeability was calculated. The calculation of the He permeability is based on the permeation amount F (cm ³ / min) of He gas per unit time, the differential pressure P (atm) applied to the dense film during He gas permeation, and the membrane area S (cm ² ) and calculated by the formula of F / (P × S). The permeation amount F (cm ³ / min) of He gas was directly read from the flow meter 14. The differential pressure P was a gauge pressure read from the pressure gauge 12. The He gas was supplied so that the differential pressure P was in the range of 0.05 to 0.90 atm. The obtained results were as shown in Table 1 and FIG.

Example A4 : Zn Permeation Test In order to evaluate the denseness of the film samples A1 to A10 from the viewpoint of Zn permeability, a Zn permeation test was performed as follows. First, a Zn transmission measuring device 10 shown in FIGS. 1A and 1B was constructed. The Zn permeation measuring apparatus 10 includes a flanged opening tube (manufactured by PTFE) in which a flange 32a is integrated with a first tank 14 formed of an L-shaped opening tube, and a second formed of an L-shaped tube. A flanged opening tube (made of PTFE) in which the flange 32b is integrated with the tank 16 is disposed so that the flanges 32a and 32b face each other, and the sample holder 12 is disposed therebetween, and the dense film held by the sample holder 12 Zn was allowed to pass through from one surface to the other.

  The assembly of the sample holder 12 and its attachment to the apparatus 10 were performed as follows. First, the adhesive 26 was applied along the outer periphery of the dense film 22 and attached to a jig 28 (made of ABS resin) having an opening at the center. As shown in FIG. 1A, silicone rubber packing is disposed on both sides of the jig 28 as sealing members 30a and 30b. Further, from the outside of the sealing members 30a and 30b, a flange 32a of a pair of flanged open tubes. , 32b. Although the dense film 22 is in the form of a composite material formed on the porous substrate 24, the dense tank 22 side is to be filled with the first aqueous solution 18 containing Zn. It was arranged to face. The flanges 32a and 32b were tightly fastened to each other by fastening means 34 using screws so that no liquid leakage occurred between them.

On the other hand, a 9 mol / L aqueous KOH solution in which 2.5 mol / L Al (OH) ₃ and 0.5 mol / L ZnO were dissolved was prepared as the first aqueous solution 18 to be put in the first tank 14. When the Zn concentration C ₁ (mol / L) of the first aqueous solution was measured by ICP emission spectroscopy, it was a value shown in Table 1. Further, as the second aqueous solution 20 to be put into the second tank 16, a 9 mol / L KOH aqueous solution in which 2.5 mol / L of Al (OH) ₃ was dissolved was prepared without dissolving ZnO. In the measuring apparatus 10 in which the sample holder 12 produced previously is incorporated, the first aqueous solution 18 and the second aqueous solution 20 are respectively injected into the first tank 14 and the second tank 16, and the dense held by the sample holder 12. Zn was permeated into the film 22. In this state, Zn permeation was performed at time t shown in Table 1, and then the liquid volume V ₂ (ml) of the second aqueous solution was measured, and the Zn concentration C ₂ (mol / L) of the second aqueous solution 20 was determined. It was measured by ICP emission spectroscopy. The Zn permeation ratio was calculated using the obtained value. The Zn permeation ratio includes the Zn concentration C ₁ (mol / L) of the first aqueous solution before the start of Zn permeation, the liquid volume V ₁ (ml) of the first aqueous solution before the start of Zn permeation, and the second concentration after the end of Zn permeation. Zn concentration C ₂ (mol / L) of the aqueous solution, the liquid volume V ₂ (ml) of the second aqueous solution after completion of Zn permeation, the permeation time t (min) of Zn, and the film area S (cm through which Zn permeates) ² ), and the calculation was performed according to the formula (C ₂ × V ₂ ) / (C ₁ × V ₁ × t × S). The obtained results were as shown in Table 1 and FIG.

Examples B1-B5
The example shown below is not an example of evaluating the Zn permeation ratio, but is a reference example showing that an LDH dense film can be formed on various porous substrates.

Example B1
(1) Production of porous substrate <Samples B1 to B3>
Boehmite (manufactured by Sasol, DISPAL 18N4-80), methylcellulose, and ion-exchanged water were weighed so that the mass ratio of (boehmite) :( methylcellulose) :( ion-exchanged water) was 10: 1: 5. Kneaded. The obtained kneaded product was subjected to extrusion molding using a hand press and molded into a size of 2.5 cm × 10 cm × thickness 0.5 cm. The obtained molded body was dried at 80 ° C. for 12 hours and then fired at the temperature shown in Table 2 for 3 hours to obtain an alumina porous substrate. After firing, the alumina porous substrate was processed into a size of 2 cm × 2 cm × 0.3 cm.

<Samples B4 and B5>
Zirconia (manufactured by Tosoh Corporation, TZ-3YS (in the case of sample B4) or TZ-8YS (in the case of sample B5)), methylcellulose, and ion-exchanged water, (zirconia): (methylcellulose): mass of (ion-exchanged water) Kneading was carried out after weighing so that the ratio was 10: 1: 5. The obtained kneaded product was subjected to extrusion molding using a hand press and molded into a size of 2.5 cm × 10 cm × thickness 0.5 cm. The obtained molded body was dried at 80 ° C. for 12 hours and then fired at the temperature shown in Table 2 for 3 hours to obtain a zirconia porous substrate. After firing, the zirconia porous substrate was processed into a size of 2 cm × 2 cm × 0.3 cm.

  With respect to the obtained porous substrate, the porosity of the surface of the porous substrate was measured by a technique using image processing, and as shown in Table 2. The porosity is measured by 1) field emission scanning electron microscope (FE-SEM) for the surface microstructure of sample B1, and scanning electron microscope (SEM, JSM-6610LV) for samples B2 to B5. , Manufactured by JEOL Co., Ltd., and observed with a predetermined acceleration voltage (1 kV for sample B1, 10 to 20 kV for samples B2 to B5), and an electron microscope image of the surface of the porous substrate (at a magnification of 10,000 times or more, sample B1) 2) Read a grayscale electron microscope image using image analysis software such as Photoshop (manufactured by Adobe), etc. 3) [Image] → [Tone correction] → [2 gradations A black and white binary image was created by the procedure of 4), and 4) the value obtained by dividing the number of pixels occupied by the black portion by the total number of pixels of the image was taken as the porosity (%). The measurement of the porosity was performed for a region of 600 nm × 600 nm with respect to the sample B1 on the surface of the porous substrate and for a region of 6 μm × 6 μm with respect to the samples B2 to B5.

  Moreover, when the average pore diameter of the porous substrate was measured, it was as shown in Table 2. In the present invention, the average pore diameter was measured by measuring the longest distance of pores based on an electron microscope (FE-SEM or SEM) image of the surface of the porous substrate. The magnification of the electron microscope (FE-SEM or SEM) image used for this measurement is 100,000 times for the sample B1, and 20000 times for the samples B2 to B5. The average pore diameter was obtained by calculating the average value for two visual fields at the top 15 points and the lower 15 points from the values, and 30 points per visual field. For length measurement, the length measurement function of FE-SEM or SEM software was used.

(2) Cleaning of porous substrate The obtained porous substrate was ultrasonically cleaned in acetone for 5 minutes, ultrasonically cleaned in ethanol for 2 minutes, and then ultrasonically cleaned in ion-exchanged water for 1 minute.

(3) As the manufacturing raw material of the raw aqueous solution, magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O, manufactured by Kanto Chemical Co., Inc.), aluminum nitrate nonahydrate (Al _{(NO 3)} 3 · 9H ₂ O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) were prepared. Weigh magnesium nitrate hexahydrate and aluminum nitrate nonahydrate so that the cation ratio (Mg ²⁺ / Al ³⁺ ) is 2 and the total metal ion molar concentration (Mg ²⁺ + Al ³⁺ ) is 0.320 mol / L. In a beaker, ion exchange water was added to make a total volume of 75 ml. After stirring the obtained solution, urea weighed at a ratio of urea / NO ₃ ⁻ = 4 was added to the solution, and further stirred to obtain a raw material aqueous solution.

(4) Film formation by hydrothermal treatment The raw material aqueous solution prepared in (3) above and the porous substrate washed in (2) above are sealed in a Teflon (registered trademark) sealed container (internal volume of 100 ml, outside is a stainless steel jacket). Both were enclosed. At this time, the base material was fixed by being floated from the bottom of a Teflon (registered trademark) sealed container, and placed horizontally so that the solution was in contact with both surfaces of the base material. Thereafter, a hydrothermal treatment was performed at a hydrothermal temperature of 70 ° C. for 168 hours (7 days) to form a layered double hydroxide alignment film on the substrate surface. After the elapse of a predetermined time, the substrate is taken out from the sealed container, washed with ion-exchanged water, dried at 70 ° C. for 10 hours, and a dense layer of layered double hydroxide (hereinafter referred to as LDH) (hereinafter referred to as membrane sample B1). ~ B5) was obtained on the substrate. The thickness of the obtained film sample was about 1.5 μm. Thus, layered double hydroxide-containing composite material samples (hereinafter referred to as composite material samples B1 to B5) were obtained. In addition, although the LDH film was formed on both surfaces of the porous substrate, the LDH film on one surface of the porous substrate was mechanically scraped to give the composite material a form as a separator.

Example B2 : Identification of a film sample With an X-ray diffractometer (RINT TTR III manufactured by Rigaku Corporation), the crystal phase of the film sample B2 was measured under the measurement conditions of voltage: 50 kV, current value: 300 mA, measurement range: 10 to 70 °. As a result of measurement, the XRD profile shown in FIG. 6 was obtained. About the obtained XRD profile, JCPDS card NO. It identified using the diffraction peak of the layered double hydroxide (hydrotalcite compound) described in 35-0964. As a result, it was confirmed that the film sample B2 was a layered double hydroxide (LDH, hydrotalcite compound). In the XRD profile shown in FIG. 6, a peak (a peak marked with a circle in FIG. 6) due to alumina constituting the porous substrate on which the film sample B2 is formed is also observed. Yes. The film samples B1 and B3 to B5 were also confirmed to be layered double hydroxides (LDH, hydrotalcite compounds) in the same manner.

Example B3 : Observation of microstructure The surface microstructure of the film sample B2 was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV. FIG. 7 shows an SEM image (secondary electron image) of the surface microstructure of the obtained film sample B2.

  Further, the cross section of the composite material sample B2 was polished by CP polishing to form a polished cross section, and the microstructure of the polished cross section was observed with a scanning electron microscope (SEM) at an acceleration voltage of 10 to 20 kV. An SEM image of the polished cross-sectional microstructure of the composite material sample B2 thus obtained is shown in FIG.

Example B4 : Measurement of porosity The porosity of the surface of the membrane of the membrane sample B2 was measured by a technique using image processing. The porosity is measured by 1) observing the surface microstructure using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV, and an electron microscope (SEM) on the surface of the film. An image (magnification of 10,000 times or more) is acquired, 2) a grayscale SEM image is read using image analysis software such as Photoshop (manufactured by Adobe), and 3) [image] → [tone correction] → [2 gradations] A black and white binary image was created by the procedure of 4), and 4) the value obtained by dividing the number of pixels occupied by the black portion by the total number of pixels of the image was taken as the porosity (%). This porosity measurement was performed on a 6 μm × 6 μm region of the membrane sample surface. As a result, the porosity of the film surface was 19.0%. Further, using the porosity of the film surface, the density D when viewed from the film surface (hereinafter referred to as the surface film density) was calculated by D = 100% − (porosity of the film surface). %Met.

  Further, the porosity of the polished cross section of the film sample B2 was also measured. The porosity of this polished cross section is also measured by the above-described film surface except that an electron microscope (SEM) image (magnification of 10,000 times or more) of the cross-section polished surface in the thickness direction of the film was obtained according to the procedure shown in Example B3. This was carried out in the same manner as the porosity. This porosity measurement was performed on the membrane portion of the membrane sample cross section. Thus, the porosity calculated from the cross-sectional polished surface of the film sample B2 is 3.5% on average (average value of the three cross-sectional polished surfaces), and a very high-density film is formed on the porous substrate. It has been confirmed.

Example B5 : Denseness determination test (reference)
In order to confirm that the membrane samples B1 to B5 have a denseness that does not have water permeability, a denseness determination test was performed as follows. First, as shown in FIG. 9A, an opening of 0.5 cm × 0.5 cm square is formed in the center on the film sample side of the composite material sample 120 (cut out to 1 cm × 1 cm square) obtained in Example B1. Silicone rubber 122 provided with 22a was bonded, and the resulting laminate was bonded between two acrylic containers 124 and 126. The bottom of the acrylic container 124 disposed on the silicon rubber 122 side is pulled out, whereby the silicon rubber 122 is bonded to the acrylic container 124 with the opening 122a open. On the other hand, the acrylic container 126 disposed on the porous substrate side of the composite material sample 120 has a bottom, and ion-exchanged water 128 is contained in the container 126. That is, by assembling the components upside down after assembly, the constituent members are arranged so that the ion exchange water 128 is in contact with the porous substrate side of the composite material sample 120. After assembling these components, the total weight was measured. As shown in FIG. 9B, the assembly was placed upside down and held at 25 ° C. for 1 week, after which the total weight was measured again. At this time, when water droplets were attached to the inner side surface of the acrylic container 124, the water droplets were wiped off. Then, the density was determined by calculating the difference in the total weight before and after the test. As a result, no change was observed in the weight of ion-exchanged water even after holding at 25 ° C. for 1 week. From this, it was confirmed that all of the membrane samples B1 to B5 (that is, the functional membrane) have high density so as not to have water permeability.

DESCRIPTION OF SYMBOLS 10 Zn transmission measuring device 12 Sample holder 14 1st tank 16 2nd tank 18 1st aqueous solution 20 2nd aqueous solution 22 Dense film 24 Porous base material 26 Adhesive 28 Jig 30a, 30b Sealing member 32a, 32b Flange 34 Fastening means 40 He permeability measurement system 42 Pressure gauge 44 Flow meter 46 Sample holder 46a Gas supply port 46b Sealed space 46c Gas discharge port 48 Dense membrane 50 Porous base material 52 Adhesive 54 Jig 56a, 56b Sealing member 58a, 58b Support member 60 Fastening means 62 Joint 64 Gas supply pipe

Claims (18)

A method for evaluating the denseness of a hydroxide ion conductive dense membrane,
A first aqueous solution containing Zn is brought into contact with one surface of the hydroxide ion conductive dense membrane, and a second aqueous solution not containing Zn or water is brought into contact with the other surface of the dense membrane, Passing Zn through the dense film for a predetermined time;
Zn concentration C ₁ of the first aqueous solution before the start of Zn permeation, liquid volume V ₁ of the first aqueous solution before the start of Zn permeation, Zn concentration C ₂ of the second aqueous solution or water after the end of Zn permeation, the end of the Zn permeation Using the second aqueous solution or water volume V ₂ , Zn permeation time t, and film area S through which Zn permeates, (C ₂ × V ₂ ) / (C ₁ × V ₁ × t × S ) To calculate the Zn permeation ratio, and evaluating the denseness of the dense film based on the Zn permeation ratio,
Including a method. The method according to claim 1, wherein the Zn concentration C1 of the first aqueous solution before Zn permeation is in the range of 0.001 to ₁ mol / L, and the permeation time of the Zn is 1 to 720 hours.   The method according to claim 1 or 2, wherein the first aqueous solution is an alkali metal hydroxide aqueous solution, and ZnO is dissolved in the alkali metal hydroxide aqueous solution.   The method according to claim 1, wherein the second aqueous solution is an alkali metal hydroxide aqueous solution in which ZnO is not dissolved.   The method according to claim 3 or 4, wherein a compound containing Al is dissolved in both the first aqueous solution and the second aqueous solution. The method further includes the step of holding the dense film in a measuring device prior to the permeation of Zn, the measuring device comprising:
A sample holder for holding the dense film in the measuring device;
A first tank that is provided on one side of the sample holder and accommodates the first aqueous solution so as to be in contact with the one surface of the dense film;
A second tank that is provided on the other side of the sample holder and accommodates the second aqueous solution in contact with the other surface of the dense membrane;
The method according to claim 1, comprising: The dense membrane having a Zn permeation ratio of 10 m ⁻² · h ⁻¹ or less is certified as being suitable for the use of a hydroxide ion conductive separator for a secondary battery, and the certified dense membrane is optionally recharged to a secondary battery. The method as described in any one of Claims 1-6 which further includes the process of using for the use of the hydroxide ion conductive separator for water. The method according to claim 7, wherein the Zn transmission rate is 1.0 m ⁻² · h ⁻¹ or less.   The method according to claim 1, wherein the dense film comprises an inorganic material and / or an organic material having hydroxide ion conductivity. Inorganic materials with the hydroxide ion conductivity, the general ^{_{formula: M 2+ 1-x M 3+}} x (OH) 2 A n- x / n · mH 2 O ( ^{wherein, M 2+} is a divalent cation , ^{M 3+} is a trivalent ^{cation, a n-n-valent} anion, n is an integer of 1 or more, x is 0.1 to 0.4, Table m is 0 or more) The method according to claim 9, comprising a layered double hydroxide. In the general formula, the ^{Mg 2+} at least ^{M 2+,} include ^{Al 3+} in ^{M 3+,} to ^{A n-OH -} containing and / or _CO ^{3 2-} The method of claim 10.   The layered double hydroxide is composed of an aggregate of a plurality of plate-like particles, and the plurality of plate-like particles are oriented in such a direction that their plate surfaces intersect the dense layer substantially perpendicularly or obliquely. The method according to claim 10 or 11, wherein   The method according to claim 1, which has a thickness of 100 μm or less.   The method according to any one of claims 1 to 13, wherein the dense membrane is prepared in the form of a composite material provided on at least one surface of a porous substrate.   The method according to claim 14, wherein the porous substrate is composed of at least one selected from the group consisting of a ceramic material, a metal material, and a polymer material.   The porous substrate is made of a ceramic material, and the ceramic material is alumina, zirconia, titania, magnesia, spinel, calcia, cordierite, zeolite, mullite, ferrite, zinc oxide, silicon carbide, aluminum nitride, and nitride. The method according to claim 15, wherein the method is at least one selected from the group consisting of silicon.   The method according to claim 14, wherein the porous substrate has an average pore diameter of 0.001 to 1.5 μm. The method according to any one of claims 14 to 17, wherein a surface of the porous substrate has a porosity of 10 to 60%.