CN109314212B

CN109314212B - Functional layer comprising layered double hydroxide and composite material

Info

Publication number: CN109314212B
Application number: CN201780037957.5A
Authority: CN
Inventors: 山本翔; 藤崎惠实; 横山昌平
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2016-06-24
Filing date: 2017-03-27
Publication date: 2022-02-08
Anticipated expiration: 2037-03-27
Also published as: CN109314212A; WO2017221498A1; WO2017221499A1; WO2017221989A1; WO2017221497A1

Abstract

The invention provides a functional layer containing a layered double hydroxide having improved strength, and a composite material including the functional layer. The functional layer of the present invention contains a layered double hydroxide, has an average porosity of 1 to 40%, and has an average pore diameter of 100nm or less.

Description

Functional layer comprising layered double hydroxide and composite material

Technical Field

The invention relates to a functional layer comprising a layered double hydroxide and to a composite material.

Background

Layered double hydroxide (hereinafter, also referred to as LDH) has exchangeable anions and H as interlayers between stacked hydroxide basic layers₂Substances of O are effectively used as catalysts, adsorbents, and dispersants in polymers for improving heat resistance.

LDH has also been attracting attention as a material for conducting hydroxide ions, and its addition to the electrolyte of an alkaline fuel cell, the catalyst layer of a zinc-air cell, has also been studied. In particular, in recent years, LDH has been proposed as a solid electrolyte separator for alkaline secondary batteries such as nickel-zinc secondary batteries and zinc-air secondary batteries, and a composite material having a functional layer containing LDH suitable for the use of the separator is known. For example, patent document 1 (international publication No. 2015/098610) discloses a composite material including a porous substrate and a functional layer containing LDH that is formed on and/or in the porous substrate and does not have water permeability, and describes: the functional layer comprising an LDH comprises a functional layer represented by the general formula: m²⁺ _1-xM³⁺ _x(OH)₂A^n- _x/n·mH₂O (in the formula, M)²⁺Is Mg²⁺Cation of equivalent valence 2, M³⁺Is Al³⁺An aliovalent 3-valent cation, A^n-Is OH^-、CO₃ ^2-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). The functional layer containing LDH disclosed in patent document 1 is densified to such an extent that it does not have water permeability, and therefore, when used as a separator, it is possible to prevent the development of zinc dendrites constituting a practical barrier of an alkaline zinc secondary battery and the intrusion of carbon dioxide from the air electrode in a zinc-air battery.

Patent document 2 (international publication No. 2016/076047) discloses a separator structure including an LDH separator that is formed by combining a porous substrate with the LDH separator, and discloses that the LDH separator has high density to the extent of gas impermeability and/or water impermeability. This document also describes: the LDH separator can have a high density as evaluated by a He permeability per unit area of 10cm/min atm or less.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2015/098610

Patent document 2: international publication No. 2016/076047

Disclosure of Invention

Recently, the inventors of the present invention have found that by setting the average porosity of the functional layer containing LDH to 1 to 40% and the average pore diameter to 100nm or less, it is possible to maintain high density of the functional layer, to improve the strength of the functional layer, and to suppress generation of cracks during drying shrinkage, in particular, to maintain density.

Accordingly, an object of the present invention is to provide a functional layer containing LDH with improved strength, and a composite material including the functional layer.

According to one aspect of the present invention, there is provided a functional layer comprising a layered double hydroxide, wherein the functional layer has an average porosity of 1 to 40% and an average pore diameter of 100nm or less.

According to another aspect of the present invention, there is provided a composite material, wherein the composite material comprises: a porous substrate; and the functional layer provided on the porous substrate and/or embedded in the porous substrate.

According to another aspect of the present invention, there is provided a battery including the functional layer or the composite material as a separator of the battery.

Drawings

Figure 1 is a schematic sectional view showing one embodiment of the LDH-containing composite material of the invention.

Fig. 2A is a cross-sectional FE-SEM image in a certain field of view of the functional layer produced in example 1 (comparative).

Fig. 2B is a cross-sectional FE-SEM image in another field of view of the functional layer fabricated in example 1 (comparative).

Fig. 3A is a cross-sectional FE-SEM image of a functional layer fabricated in example 3 in a certain field of view.

Fig. 3B is a cross-sectional FE-SEM image in another field of view of the functional layer fabricated in example 3.

FIG. 4A is a conceptual diagram showing an example of the He transmittance measurement system used in examples 1 to 8.

FIG. 4B is a schematic sectional view of the sample holder and its peripheral structure used in the measurement system shown in FIG. 4A.

Fig. 5A is a surface SEM image in a certain field of view of the functional layer produced in example 1 (comparative).

Fig. 5B is a surface SEM image in another field of view of the functional layer fabricated in example 1 (comparative).

Fig. 6A is a surface SEM image in a certain field of view of the functional layer produced in example 3.

Fig. 6B is a surface SEM image in another field of view of the functional layer fabricated in example 3.

Detailed Description

Functional layer containing LDH and composite material

The functional layer of the present invention is a layer comprising a Layered Double Hydroxide (LDH), and the LDH-containing functional layer has an average porosity of 1 to 40% and an average pore diameter of 100nm or less. By setting the average porosity of the functional layer containing LDH to 1 to 40% and the average pore diameter to 100nm or less in this way, high density of the functional layer can be maintained, and the strength of the functional layer can be increased. That is, an average pore diameter of 100nm or less means: the pores contained in the functional layer are of a size on the nanometer level. And, it is considered that: by introducing such nano pores into the functional layer, the shrinkage stress during drying is relaxed. In this regard, if the average porosity is less than 1%, stress relaxation is insufficient, and cracks are likely to occur. On the other hand, if the average porosity is more than 40%, the denseness of the functional layer cannot be maintained. Even if the average pore diameter is larger than 100nm, the dispersibility of pores is deteriorated, and as a result, stress relaxation is insufficient, and cracks are likely to occur. According to the functional layer of the present invention, these disadvantages can be favorably overcome. It is preferable that the functional layer has no cracks and that cracks are not generated even when the functional layer is dried at 70 c for 20 hours.

The functional layer has an average porosity of 1 to 40%, preferably 1 to 35%, and more preferably 5 to 35%. When the content is within these ranges, the strength of the functional layer can be further improved while maintaining high density of the functional layer. In particular, it is possible to more effectively realize: the occurrence of cracks at the time of drying shrinkage is suppressed, and the denseness is maintained. The measurement of the average porosity of the functional layer can be performed by: a) grinding the cross section of the functional layer by using a cross section polishing machine (CP); b) taking cross-sectional images of the functional layer in 2 fields of view at 50000 times magnification by using an FE-SEM (field emission scanning electron microscope); c) calculating the porosity of each of the 2 fields of view using image detection software (for example, HDevelop, MVTecSoftware) based on the image data of the acquired cross-sectional image; d) the average value of the obtained porosities was obtained.

The average pore diameter in the functional layer is less than 100nm, preferably 10-50 nm, and more preferably 20-40 nm. The functional layer can maintain high density and further improve the strength of the functional layer. In particular, it is possible to more effectively realize: the occurrence of cracks at the time of drying shrinkage is suppressed, and the denseness is maintained. The determination of the average pore diameter in the functional layer can be carried out by: a) grinding the cross section of the functional layer by using a cross section polishing machine (CP); b) a cross-sectional image of the functional layer was taken at 50000 times magnification using an FE-SEM (field emission scanning electron microscope); c) measuring the pore diameter by measuring the longest distance of the pore based on the obtained sectional image; d) all the obtained pore diameters are arranged according to the size sequence, from the near to the far of the average value, 10 numerical values above the average value and 10 numerical values below the average value are taken, 20 numerical values are taken in each visual field in total, and the average value of 2 visual fields is calculated. And (4) measuring length by using the length measuring function of the software of the SEM.

The functional layer comprises a Layered Double Hydroxide (LDH). It is generally known that: LDHs are composed of multiple hydroxide base layers and interlayers interposed between these multiple hydroxide base layers. The hydroxide base layer is mainly composed of a metal element (typically, metal ions) and OH groups. The interlayer of the LDH contained in the functional layer is composed of an anion and H₂And O. The anion is an anion having a valence of 1 or more, preferably an ion having a valence of 1 or 2. Preferably, the anion in the LDH comprises OH^-And/or CO₃ ^2-. However, since an electrolyte solution for an alkaline secondary battery (for example, a metal-air battery or a nickel-zinc battery) using LDH is required to have high hydroxide ion conductivity, it is required to use a strongly basic KOH aqueous solution having a pH of about 14. Therefore, LDH is required to have high alkali resistance that hardly deteriorates even in a strongly alkaline electrolyte such as this. Therefore, the LDH in the present invention is preferably an LDH whose surface microstructure and crystal structure are not changed by the alkali resistance evaluation as described later, and the composition thereof is not particularly limited. In addition, LDH has excellent ion conductivity due to its inherent properties, as described above.

Specifically, from the viewpoint of excellent alkali resistance, it is preferable that the LDH contained in the functional layer is not changed in both the surface microstructure and the crystal structure when immersed in a 6mol/L aqueous potassium hydroxide solution containing zinc oxide at a concentration of 0.4mol/L at 70 ℃ for 3 weeks (i.e., 504 hours). It may be preferred that: the presence or absence of a change in the surface microstructure is determined by the surface microstructure obtained by SEM (scanning electron microscope), and the presence or absence of a change in the crystal structure is determined by crystal structure analysis (for example, the presence or absence of a shift in the (003) peak derived from LDH) by XRD (X-ray diffraction). Potassium hydroxide is a representative strong base substance, and the composition of the potassium hydroxide aqueous solution corresponds to a representative strong base electrolyte of an alkaline secondary battery. Therefore, the above evaluation method of immersing the electrolyte in such a strongly alkaline electrolyte solution at a high temperature of up to 70 ℃ for a period of up to 3 weeks is said to be a severe alkali resistance test. LDHs for alkaline secondary batteries are required to have high alkali resistance that hardly deteriorates even in strongly alkaline electrolytes. In this regard, the functional layer of the present embodiment has excellent alkali resistance, that is, neither the surface microstructure nor the crystal structure is changed by such a severe alkali resistance test. Even so, the functional layer of the present aspect can exhibit high ion conductivity suitable for use as a separator for an alkaline secondary battery due to the properties inherent to LDH. That is, according to this aspect, the functional layer containing LDH having not only excellent ion conductivity but also excellent alkali resistance can be provided.

According to a preferred embodiment of the present invention,the hydroxide base layer of LDH is composed of Ni, Ti, OH groups, and inevitable impurities according to circumstances. The interlayer of the LDH is composed of an anion and H as described above₂And O. The alternate laminated structure of the hydroxide base layer and the intermediate layer itself is substantially the same as that of a conventionally known LDH, but the functional layer of this scheme is constituted mainly of Ni, Ti, and OH groups to thereby be able to exhibit excellent alkali resistance. The reason is not necessarily determined, but is considered to be due to: no element (e.g. Al) which is believed to be readily dissolved in the alkaline solution is intentionally or actively added to the LDH in this scheme. Even so, the functional layer of the present aspect can exhibit high ion conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH may take the form of nickel ions. Typical for nickel ions in LDH is believed to be Ni²⁺However, it may be Ni³⁺And other valences of nickel ions, and therefore, is not particularly limited. Ti in LDH may take the form of titanium ions. With respect to titanium ions in LDH, Ti is considered to be typical⁴⁺However, it may be Ti³⁺And other valence titanium ions, and therefore, is not particularly limited. The inevitable impurities are any elements that may be inevitably mixed in the production process, and may be derived from the starting material or the substrate and mixed into the LDH, for example. As mentioned above, the valences of Ni and Ti are not necessarily determined, and therefore, it is not practical or possible to specify LDHs strictly by the general formula. Assuming that the hydroxide base layer consists essentially of Ni²⁺、Ti⁴⁺And OH groups, the basic composition of the corresponding LDH may consist of the general formula: ni²⁺ _1-xTi⁴⁺ _x(OH)₂A^n- _2x/n·mH₂O (in the formula, A)^n-Is an anion having a valence of n, n is an integer of 1 or more, preferably 1 or 2, 0 < x < 1, preferably 0.01. ltoreq. x.ltoreq.0.5, and m is 0 or more, typically a real number exceeding 0, or 1 or more). However, the above formula should be understood as merely "consisting essentially of", and should be understood as: ni²⁺Or Ti⁴⁺The elements can be substituted with other elements or ions (including other valences of the same element) to the extent that the basic properties of the LDH are not compromisedElement or ion(s), element or ion(s) that may be inevitably mixed in the production process).

According to another preferred embodiment of the invention, the hydroxide base layer of the LDH comprises Ni, Al, Ti and OH groups. The intermediate layer is composed of an anion and H as described above₂And O. The alternate layered structure of the hydroxide base layer and the intermediate layer itself is substantially the same as that of a conventionally known LDH, but the functional layer of this embodiment can exhibit excellent alkali resistance by constituting the hydroxide base layer of the LDH with a predetermined element or ion including Ni, Al, Ti, and OH groups. The reason is not necessarily clear, but the LDH of this embodiment is considered to be caused by: it has been thought that Al which is easily eluted in an alkaline solution is difficult to elute in an alkaline solution due to some interaction with Ni and Ti. Even so, the functional layer of the present aspect can exhibit high ion conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH may take the form of nickel ions. Typical for nickel ions in LDH is believed to be Ni²⁺However, it may be Ni³⁺And other valences of nickel ions, and therefore, is not particularly limited. Al in LDH may take the form of aluminium ions. With respect to aluminum ions in LDH, Al is considered to be typical³⁺However, the number is not particularly limited, since other valences may be used. Ti in LDH may take the form of titanium ions. With respect to titanium ions in LDH, Ti is considered to be typical⁴⁺However, it may be Ti³⁺And other valence titanium ions, and therefore, is not particularly limited. The hydroxide base layer may contain Ni, Al, Ti, and OH groups, and may contain other elements or ions. However, the hydroxide base layer preferably contains Ni, Al, Ti, and OH groups as main constituents. That is, it is preferable that the hydroxide base layer mainly contains Ni, Al, Ti, and OH groups. Thus, a typical scheme for the hydroxide base layer is: consists of Ni, Al, Ti, OH groups and inevitable impurities according to the situation. The inevitable impurities are any elements that may be inevitably mixed in the production process, and may be derived from the starting material or the substrate and mixed into the LDH, for example. As described above, the valence numbers of Ni, Al and Ti are not always determined, and thereforeIt is not practical or possible to specify LDHs strictly in the general formula. Assuming that the hydroxide base layer consists essentially of Ni²⁺、Al³⁺、Ti⁴⁺And OH groups, the basic composition of the corresponding LDH may consist of the general formula: ni²⁺ _1-x-yAl³⁺ _xTi⁴⁺ _y(OH)₂A^n- _(x+2y)/n·mH₂O (in the formula, A)^n-Is an anion having a valence of n, n is an integer of 1 or more, preferably 1 or 2, 0 < x < 1, preferably 0.01. ltoreq. x.ltoreq.0.5, 0 < y < 1, preferably 0.01. ltoreq. y.ltoreq.0.5, 0 < x + y < 1, m is 0 or more, typically a real number exceeding 0, or 1 or more). However, the above formula should be understood as merely "consisting essentially of", and should be understood as: ni²⁺、Al³⁺、Ti⁴⁺The elements can be replaced with other elements or ions (including elements or ions of other valences of the same element, elements or ions that may be inevitably incorporated in the manufacturing process) to the extent that the basic properties of the LDH are not compromised.

The functional layer (in particular the LDH contained in the functional layer) preferably has hydroxide ion conductivity. In particular, the functional layer preferably has an ionic conductivity of 0.1mS/cm or more, more preferably 0.5mS/cm or more, and still more preferably 1.0mS/cm or more. The higher the ionic conductivity, the better, and its upper limit value is not particularly limited, and is, for example, 10 mS/cm. Such high ionic conductivity is particularly suitable for battery applications. For example, it is desired to reduce the resistance of LDH by making it thin for practical use, and according to this aspect, it is possible to provide a functional layer containing LDH with a low resistance ideally, and therefore, LDH is particularly advantageous for application as a solid electrolyte separator to alkaline secondary batteries such as zinc-air batteries and nickel-zinc batteries.

Preferably, the functional layer is provided on the porous substrate and/or embedded in the porous substrate. That is, according to a preferred embodiment of the present invention, there is provided a composite material including a porous substrate and a functional layer provided on the porous substrate and/or embedded in the porous substrate. For example, like the composite 10 shown in fig. 1, the functional layer 14 may: a part of the porous substrate 12 is embedded in the porous substrate 12, and the remaining part is provided on the porous substrate 12. At this time, it can be said that: the portion of the functional layer 14 above the porous substrate 12 is a membrane-like portion composed of an LDH membrane, and the portion of the functional layer 14 embedded in the porous substrate 12 is a composite portion composed of the porous substrate and the LDH. The typical morphology of the composite part is: the pores of the porous substrate 12 are filled with LDH. Alternatively, the functional layer may be embedded in the entire thickness or the entire thickness of the porous substrate.

The porous substrate in the composite material of the present invention is preferably capable of forming a functional layer containing LDH on and/or in the porous substrate, and the material and porous structure thereof are not particularly limited. The functional layer containing LDH is typically formed on and/or in the porous substrate, but the functional layer containing LDH may be formed on a non-porous substrate, and the non-porous substrate may be made porous by various known methods. In short, the porous base material is preferably a porous structure having water permeability, and is preferably a structure capable of constituting a functional layer accessible to an electrolytic solution when incorporated as a battery separator in a battery.

The porous substrate is preferably composed of at least 1 selected from the group consisting of a ceramic material, a metal material, and a polymer material, and more preferably composed of at least 1 selected from the group consisting of a ceramic material and a polymer material. The porous substrate is more preferably 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, and any combination thereof, more preferably alumina, zirconia, titania, and any combination thereof, and particularly preferably alumina, zirconia (for example, yttria-stabilized zirconia (YSZ)), and a combination thereof. When these porous ceramics are used, an LDH-containing functional layer having excellent denseness is easily formed. Preferable examples of the metal material include aluminum, zinc, and nickel. Preferable examples of the polymer material include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrophilized fluororesin (tetrafluoro resin: PTFE and the like), cellulose, nylon, polyethylene, and any combination thereof. Each of the above-mentioned preferable materials has alkali resistance as resistance to a battery electrolyte.

The porous base material preferably has an average pore diameter of 100 μm or less at the maximum, more preferably 50 μm or less at the maximum, for example, typically 0.001 to 1.5 μm, more typically 0.001 to 1.25 μm, further typically 0.001 to 1.0 μm, particularly typically 0.001 to 0.75 μm, most typically 0.001 to 0.5. mu.m. By setting the pore size in these ranges, the porous substrate can have desired water permeability and strength as a support, and can form a functional layer containing LDH which is dense to such an extent that it does not have water permeability. In the present invention, the average pore diameter can be measured by measuring the longest distance of pores based on an 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, all the obtained gas pore diameters are arranged in order of size, 15 values of the average value or more and 15 values of the average value or less are taken from the near side to the far side of the average value, 30 values are taken for each field in total, and the average value of 2 fields is calculated, whereby the average gas pore diameter can be obtained. For the measurement, a length measuring function of software of SEM, image analysis software (for example, Photoshop, Adobe, inc.) and the like can be used.

The porous base material preferably has a porosity of 10 to 60%, more preferably 15 to 55%, and still more preferably 20 to 50%. By setting the pore size in these ranges, the porous substrate can have desired water permeability and strength as a support, and can form a functional layer containing LDH which is dense to such an extent that it does not have water permeability. The porosity of the porous substrate can be measured preferably by the archimedes method.

The functional layer preferably has no breathability. That is, the functional layer is preferably densified by LDH to the extent that it does not have gas permeability. In the present specification, "not having air permeability" means: as described in patent document 2 (international publication No. 2016/076047), even when helium gas is brought into contact with one surface side of an object to be measured (i.e., a functional layer or a composite material) in water at a pressure difference of 0.5atm, bubbles generated by the helium gas are not observed from the other surface side. Thus, the functional layer or the composite material as a whole selectively passes only hydroxide ions due to its hydroxide ion conductivity, and can function as a battery separator. When LDH is considered to be used as a solid electrolyte separator for a battery, the LDH compact in a block form has a problem of high resistance, but in a preferred embodiment of the present invention, strength can be imparted by the porous substrate, and therefore, the functional layer containing LDH can be made thin to achieve low resistance. Further, since the porous substrate can have water permeability and air permeability, when used as a solid electrolyte separator for a battery, the porous substrate can have a structure in which the electrolyte solution can reach the functional layer containing LDH. That is, the functional layer containing LDH and the composite material of the present invention can be very useful as a solid electrolyte separator applicable to various battery applications such as a metal-air battery (e.g., a zinc-air battery) and other various zinc secondary batteries (e.g., a nickel-zinc battery).

The He transmittance per unit area of the functional layer or the composite material having the functional layer is preferably 10cm/min atm or less, more preferably 5.0cm/min atm or less, and still more preferably 1.0cm/min atm or less. It can be said that: the functional layer having He transmittance in such a range has very high denseness. Therefore, when the functional layer having a He permeability of 10cm/min atm or less is used as a separator in an alkaline secondary battery, substances other than hydroxide ions can be prevented from passing therethrough at a high level. For example, in the case of a zinc secondary battery, zinc ions or zincate ions can be very effectively inhibited from permeating through the electrolyte. In principle, it is considered that: by thus remarkably suppressing Zn permeation, the growth of zinc dendrites can be effectively suppressed when used in a zinc secondary battery. He transmittance was measured by the following procedure: the method for manufacturing a semiconductor device includes a step of supplying He gas to one surface of a functional layer and allowing the He gas to pass through the functional layer, and a step of calculating He transmittance and evaluating the denseness of the functional layer. He transmittance is calculated from the formula F/(P × S) using the pressure difference P applied to the functional layer when the He gas has a transmittance of F, He per unit time and the membrane area S through which He gas has permeated. By using He gas in this way, gas is generatedThe evaluation of the permeability enables the evaluation of the denseness at an extremely high level, and as a result, the evaluation of the high denseness which makes the substances other than the hydroxide ions (particularly Zn which causes the zinc dendrite growth) as impervious as possible (only a very small amount of penetration) is effective. This is because: he gas has the smallest constituent unit among a variety of atoms or molecules that can constitute the gas, and the reactivity is very low. That is, He does not form molecules, but He gas is composed of He atoms alone. In this regard, since hydrogen is derived from H₂Since the molecular structure is such that He atomic monomer is relatively small as a gas constituent unit. Because of H₂The gas is after all a combustible gas and is therefore dangerous. Further, by using the index of He gas transmittance defined by the above formula, objective evaluation of denseness can be easily performed regardless of various sample sizes and measurement conditions. Thus, it is possible to evaluate whether or not the functional layer has sufficiently high denseness suitable for a separator for a zinc secondary battery, simply, safely, and efficiently. The He transmittance can be preferably measured according to the procedure shown in evaluation 3 of example described later.

The thickness of the functional layer is preferably 100 μm or less, more preferably 75 μm or less, still more preferably 50 μm or less, particularly preferably 25 μm or less, and most preferably 5 μm or less. By making the thickness thin, the resistance of the functional layer can be reduced. When the functional layer is formed as an LDH film on the porous substrate, the thickness of the functional layer corresponds to the thickness of the film portion formed of the LDH film. In the case where the functional layer is embedded in the porous substrate, the thickness of the functional layer corresponds to the thickness of the composite portion formed of the porous substrate and the LDH. When the functional layer is formed on or in the porous substrate, the functional layer corresponds to the total thickness of the membrane portion (LDH membrane) and the composite portion (porous substrate and LDH). In short, if the thickness is as described above, a desired low resistance suitable for practical use in battery applications and the like can be achieved. The lower limit of the thickness of the LDH-oriented film is not particularly limited, and therefore, the thickness is preferably 1 μm or more, more preferably 2 μm or more, in order to ensure a certain degree of compactness desired as a functional film such as a separator.

The method for producing the functional layer containing LDH and the composite material is not particularly limited, and can be produced by appropriately changing various conditions of a known method for producing a functional layer containing LDH and a composite material (for example, see patent documents 1 and 2). For example, (1) preparing a porous substrate; (2) applying a titania sol or a mixed sol of alumina and titania to a porous base material, and performing heat treatment to form a titania layer or an alumina-titania layer; (3) immersing the porous base material in a solution containing nickel ions (Ni)²⁺) And a feed aqueous solution of urea; (4) the porous substrate is subjected to hydrothermal treatment in an aqueous raw material solution to form a functional layer containing LDH on and/or in the porous substrate, thereby producing a functional layer containing LDH and a composite material. In particular, in the step (2), the titanium oxide layer or the alumina/titania layer is formed on the porous substrate, so that not only the starting material of LDH is supplied, but also the starting point of LDH crystal growth is made to function, and a highly densified LDH-containing functional layer can be uniformly formed on the surface of the porous substrate without unevenness. In the step (3), ammonia is generated in the solution by hydrolysis of urea due to the presence of urea, the pH is increased, and the coexisting metal ions form hydroxides, thereby obtaining LDH. Since the hydrolysis is accompanied by the generation of carbon dioxide, LDH whose anion is a carbonate ion can be obtained.

Particularly preferred methods for producing a functional layer and composite material comprising LDH have the following characteristics, which are believed to contribute to the various characteristics of the functional layer of the invention.

a) As the mixed sol of alumina and titania used in the step (2), a mixed sol (for example, a mixed sol containing an amorphous alumina solution (Al-ML15, manufactured by polywood chemicals) and a titania sol solution (M-6, manufactured by polywood chemicals)) is used;

b) in the step (2), the heat treatment temperature of the sol applied to the porous substrate is set to be low, preferably 70 to 300 ℃ (for example, 150 ℃);

c) in the step (3), nickel ions (Ni) are supplied in the form of nickel nitrate²⁺) At this time, according to urea/NO₃ ^-The molar ratio of (a) to (b), preferably 8 to 32 (e.g., 32), with urea;

d) the hydrothermal treatment in the step (4) is carried out at a relatively low temperature, preferably 70 to 150 ℃ (e.g., 120 ℃), and for a relatively short time, preferably 10 hours or longer, and more preferably 10 to 40 hours (e.g., 24 hours); and/or

e) After the step (4), the functional layer is washed with ion-exchanged water, and then dried at a relatively low temperature, preferably room temperature to 70 ℃ (e.g., room temperature).

Examples

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

Example 1(comparison)

Various functional layers and composite materials including LDHs containing Ni, Al, and Ti were produced and evaluated by the following procedure.

(1) Production of porous substrate

70 parts by weight of a dispersion medium (xylene: butanol: 1), 11.1 parts by weight of a binder (polyvinyl butyral: BM-2, manufactured by WANCH CHEMICAL CO., LTD.), 5.5 parts by weight of a plasticizer (DOP: Rheodol SP-O30, manufactured by Kao corporation) and 2.9 parts by weight of a dispersant (RHEODOL SP-O30, manufactured by Kao corporation) were mixed with 100 parts by weight of zirconia powder (TZ-8 YS, manufactured by Tosoh Corp.), and the mixture was stirred under reduced pressure to remove bubbles, thereby obtaining a slurry. The slurry was molded in a sheet form on a PET film to a thickness of 220 μm after drying using a casting machine to obtain a sheet-like molded article. The molded article thus obtained was cut into pieces of 2.0 cm. times.2.0 cm. times.0.022 cm in thickness, and fired at 1100 ℃ for 2 hours to obtain a porous substrate made of zirconia.

The porosity of the obtained porous substrate was measured by the archimedes method, and the result was 40%.

The average pore diameter of the porous substrate was measured, and found to be 0.2. mu.m. The average pore diameter is measured by measuring the longest distance of pores based on an electron microscope (SEM) image of the surface of the porous substrate. The magnification of an electron microscope (SEM) image used for this measurement was 20000 times, and all the obtained gas pore diameters were arranged in order of size, and from near to far from the average, 15 values above the average and 15 values below the average were taken, and 30 values were taken for each field in total, and the average of 2 fields was calculated to obtain the average gas pore diameter. In the length measurement, the length measurement function of software of SEM is used.

(2) Coating alumina-titania sol on porous base material

An amorphous alumina solution (Al-ML15, manufactured by Polywood chemical Co., Ltd.) and a titania sol solution (M-6, manufactured by Polywood chemical Co., Ltd.) were mixed in a weight ratio of the solutions of 1: 1, mixing to prepare a mixed sol. 0.2ml of the mixed sol was applied to the porous zirconia substrate obtained in the above (1) by spin coating. In the spin coating method, the mixed sol was dropped on a substrate rotating at 4000rpm, the rotation was stopped after 5 seconds, and the substrate was allowed to stand on a heating plate heated to 100 ℃ and dried for 1 minute. Then, heat treatment was performed at 150 ℃ using an electric furnace. The thickness of the layer thus formed is about 1 μm.

(3) Preparation of aqueous solution of raw Material

Nickel nitrate hexahydrate (Ni (NO) was prepared as a raw material₃)₂·6H₂O, manufactured by Kanto chemical Co., Ltd.), and urea ((NH)₂)₂CO manufactured by Sigma Aldrich). Nickel nitrate hexahydrate was weighed at 0.03mol/L and placed in a beaker, and ion-exchanged water was added thereto to make the total amount 75 ml. After stirring the resulting solution, the urea/NO ratio is adjusted₃ ^-Urea was added to the solution in a ratio of (molar ratio) 32, and the mixture was further stirred to obtain a raw material aqueous solution.

(4) Film formation by hydrothermal treatment

The aqueous solution of the raw material prepared in (3) above and the base material prepared in (2) above were sealed in a closed container (autoclave container, inner volume 100ml, outer side stainless steel sleeve) made of Teflon (registered trademark). At this time, the substrate was floated and fixed from the bottom of a closed container made of teflon (registered trademark), and horizontally set so that the solution contacted both surfaces of the substrate. Then, by performing hydrothermal treatment at a hydrothermal temperature of 120 ℃ for 8 hours, LDH is formed on the surface and inside of the substrate. After a predetermined period of time has elapsed, the substrate is taken out of the closed container, washed with ion-exchanged water, left to stand at room temperature for 12 hours, and dried to obtain a functional layer containing LDH as a part of which is embedded in the porous substrate. The thickness of the obtained functional layer (including the thickness of the portion embedded in the porous substrate) was about 2 μm.

Example 2

A functional layer and a composite material were produced by the same procedure as in example 1, except that the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was set to 12 hours.

Example 3

A functional layer and a composite material were produced by the same procedure as in example 1, except that the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was set to 22 hours.

Example 4

A functional layer and a composite material were produced by the same procedure as in example 1, except that the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was 30 hours.

Example 5

A functional layer and a composite material were produced by the same procedure as in example 1, except that the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was set to 40 hours.

Example 6(comparison)

A functional layer and a composite material were produced by the same procedure as in example 1, except that the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was set to 50 hours.

Example 7(comparison)

A functional layer and a composite material were produced by the same procedure as in example 1, except that AM-15 (manufactured by polywood chemical) was used instead of M-6 as the titania sol solution and the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was 30 hours when the alumina-titania sol was applied to the porous substrate.

Example 8(comparison)

A functional layer and a composite material were produced by the same procedure as in example 1, except that AM-15 (manufactured by polywood chemical) was used instead of M-6 as the titania sol solution and the hydrothermal treatment time in the step of forming a film by hydrothermal treatment was set to 40 hours when the alumina-titania sol was applied to the porous substrate.

< evaluation >

The functional layer or the composite material obtained was subjected to the following various evaluations.

Evaluation 1: measurement of average porosity

The functional layer was cross-section polished by a cross-section polisher (CP), and cross-sectional images of the functional layer were taken at 50000 times magnification in 2 fields of view by FE-SEM (ULTRA55, manufactured by Carl Zeiss). Based on the image data, the porosity of each of the 2 fields was calculated by using image detection software (HDevelop, MVTecSoftware), and the average value of the porosities was defined as the average porosity. The results are shown in Table 1. Fig. 2A and 2B show cross-sectional FE-SEM images of the functional layer of example 1 (comparative), and fig. 3A and 3B show cross-sectional FE-SEM images of the functional layer of example 3.

Evaluation 2: mean pore size determination

The longest distance of the pores was measured based on the sectional image of the functional layer obtained in evaluation 1, and thereby the pore diameter was measured. Arranging all the obtained air apertures according to the size sequence, taking 10 values above the average value and 10 values below the average value from near to far from the average value, taking 20 values in each visual field in total, and calculating the average value of 2 visual fields to obtain the average air aperture. The length measurement function of the software of the SEM was used. The results are shown in Table 1.

Evaluation 3: he permeation measurement

In order to evaluate the denseness of the functional layer from the viewpoint of He permeability, He permeability test was performed as follows. First, He transmittance measurement system 310 shown in fig. 4A and 4B was constructed. He transmittance measurement system 310 is constituted by: he gas from a gas cylinder filled with He gas is supplied to the sample holder 316 via a pressure gauge 312 and a flow meter 314 (digital flow meter), and is discharged through one surface of the functional layer 318 held by the sample holder 316 to the other surface.

The sample holder 316 has a structure including a gas supply port 316a, a closed space 316b, and a gas discharge port 316c, and is assembled as follows. First, an adhesive 322 is applied along the outer periphery of the functional layer 318, and attached to a jig 324 (made of ABS resin) having an opening at the center. The upper and lower ends of the jig 324 are provided with butyl rubber seals as

seal members

326a, 326b, and are held by

support members

328a, 328b (made of PTFE) having openings formed by flanges from the outside of the

seal members

326a, 326 b. Thus, the functional layer 318, the jig 324, the seal member 326a, and the support member 328a define a sealed space 316 b. The functional layer 318 is in the form of a composite material formed on the porous substrate 320, and is disposed so that the functional layer 318 side faces the gas supply port 316 a. The

support members

328a, 328b are fastened to each other by a fastening mechanism 330 using screws so that He gas does not leak from portions other than the gas discharge port 316 c. The gas supply pipe 334 is connected to the gas supply port 316a of the thus assembled sample holder 316 via the connector 332.

Next, He gas is supplied into the He transmittance measurement system 310 through the gas supply tube 334, and is allowed to permeate through the functional layer 318 held in the sample holder 316. At this time, the gas supply pressure and flow rate are monitored by the pressure gauge 312 and the flow meter 314. He gas permeation is carried out for 1 to 30 minutes, and then He permeation rate is calculated. Calculation of He transmittance the permeation amount F (cm) of He gas per unit time was used³Min), the pressure difference P (atm) applied to the functional layer during permeation of He gas, and the membrane area S (cm) through which He gas permeates²) And calculated from the formula F/(P × S). Permeation amount F (cm) of He gas³/min) is read directly from flow meter 314. In addition, the differential pressure P uses the slave pressureThe gauge pressure read by the force gauge 312. The He gas is supplied at a pressure difference P in the range of 0.05 to 0.90 atm. The results are shown in Table 1.

Evaluation 4: drying test

The functional layer was dried in a desiccator at 70 ℃ for 20 hours, and then observed with a Scanning Electron Microscope (SEM) to evaluate the presence or absence of crack generation. In addition, He transmittance of the functional layer after drying was measured in the same manner as in evaluation 3. The results are shown in Table 1. Fig. 5A and 5B show surface SEM images of the functional layer of example 1 (comparative), and fig. 6A and 6B show surface SEM images of the functional layer of example 3.

Evaluation 5: authentication of functional layers

Using an X-ray diffraction apparatus (RINT TTR III, manufactured by chem corporation), under the conditions of voltage: 50kV, current value: 300mA, measurement range: and under the measuring condition of 10-70 degrees, measuring the crystalline phase of the functional layer to obtain an XRD (X-ray diffraction) pattern. The obtained XRD pattern was identified by using the diffraction peak of LDH (hydrotalcite-like compound) described in JCPDS Card NO. 35-0964. And (4) result identification: all the functional layers obtained in examples 1 to 8 were LDH (hydrotalcite-like compound).

Evaluation 6: elemental analysis Evaluation (EDS)

And (4) performing section grinding on the functional layer by using a section polishing machine (CP). Cross-sectional images of the functional layer were acquired in 1 visual field at a magnification of 10000 times by FE-SEM (ULTRA55, manufactured by Carl Zeiss). The LDH membrane on the surface of the substrate and the LDH moiety inside the substrate in the cross-sectional image (spot analysis) were subjected to elemental analysis under an accelerated voltage of 15kV using an EDS analyzer (NORAN System SIX, manufactured by Thermo Fisher Scientific). As a result: from the LDHs included in the functional layers obtained in examples 1 to 8, C, Al, Ti and Ni were detected as LDH-constituting elements. That is, Al, Ti and Ni are constituent elements of the hydroxide basic layer, while C and CO, which is an anion constituting the interlayer of LDH₃ ^2-And correspondingly.

Evaluation 7: evaluation of alkali resistance

Zinc oxide was dissolved in a 6mol/L aqueous potassium hydroxide solution to obtain a 6mol/L aqueous potassium hydroxide solution containing zinc oxide at a concentration of 0.4 mol/L. 15ml of the aqueous potassium hydroxide solution thus obtained was placed in a closed container made of Teflon (registered trademark). The composite material with the size of 1cm × 0.6cm was placed on the bottom of the closed container with the functional layer facing upward, and the lid was closed. Then, after maintaining at 70 ℃ for 3 weeks (i.e., 504 hours), the composite material was taken out of the closed vessel. The removed composite was allowed to dry at room temperature for 1 night. The microstructure of the obtained sample was observed by SEM, and the crystal structure thereof was observed by XRD. At this time, the change in crystal structure was determined by the presence or absence of shift of the (003) peak derived from LDH in the XRD pattern. As a result: in any of examples 1 to 8, no change in the surface microstructure and crystal structure was observed.

[ TABLE 1 ]

Indicates comparative examples.

Claims

1. A functional layer which is a functional layer comprising a layered double hydroxide, wherein,

the functional layer has an average porosity of 1 to 40% and an average pore diameter of 23 to 50nm,

the layered double hydroxide is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the hydroxide basic layers, wherein the hydroxide basic layers are composed of Ni, Ti and OH groups or are composed of Ni, Ti, OH groups and unavoidable impurities, and the intermediate layer is composed of anions and H₂O, or, alternatively,

the layered double hydroxide is composed of a plurality of hydroxide base layers containing Ni, Al, Ti and OH groups and an intermediate layer interposed between the plurality of hydroxide base layers, the intermediate layer being composed of an anion and H₂And O.

2. The functional layer of claim 1, wherein,

the functional layer had no cracks, and no cracks were generated even when the functional layer was dried at 70 ℃ for 20 hours.

3. The functional layer of claim 1, wherein,

when the layered double hydroxide was immersed in a 6mol/L aqueous potassium hydroxide solution containing zinc oxide at a concentration of 0.4mol/L at 70 ℃ for 3 weeks, neither the surface microstructure nor the crystal structure was changed.

4. The functional layer according to any of claims 1 to 3, wherein,

the functional layer has a He transmittance per unit area of 10cm/min atm or less.

5. The functional layer according to any of claims 1 to 3, wherein,

the functional layer has a thickness of 100 μm or less.

6. The functional layer according to any of claims 1 to 3, wherein,

the functional layer has a thickness of 50 μm or less.

7. The functional layer according to any of claims 1 to 3, wherein,

the functional layer has a thickness of 5 μm or less.

8. A composite material, wherein,

the composite material comprises:

a porous substrate; and

the functional layer according to any one of claims 1 to 7, which is provided on the porous substrate and/or embedded in the porous substrate.

9. The composite material of claim 8,

the porous substrate is composed of at least 1 selected from the group consisting of a ceramic material, a metal material, and a polymer material.

10. The composite material according to claim 8 or 9,

the composite material has a He transmittance per unit area of 10cm/min atm or less.

11. A battery comprising, as a separator thereof, the functional layer according to any one of claims 1 to 7 or the composite material according to any one of claims 8 to 10.