WO2018163353A1 - Method for manufacturing separator/air electrode assembly - Google Patents

Abstract

Provided is a method for manufacturing a separator/air electrode assembly in which it is possible to carry out direct bonding while ensuring a desired adhesive strength of an air electrode layer containing LDH and CNT with respect to an LDH separator. This method includes: a step for preparing a layered double hydroxide (LDH) powder; a step for obtaining a metal oxide powder by baking the LDH powder at 400-850°C for 1-10 hours; a step for mixing a metal oxide powder, carbon nanotubes, and a solvent to form a paste or slurry; a step for applying the paste or slurry to the surface of the LDH separator; and a step for carrying out steam treatment of the LDH separator coated with the paste or the slurry, converting a metal oxide to LDH, and thereby obtaining an air electrode layer on the LDH separator.

Description

Method for manufacturing separator / air electrode composite

The present invention relates to a method for producing a separator / air electrode composite.

As an air electrode for a metal-air battery, an electrode including an electron conductive material as a main component and a layered double hydroxide (LDH) and a binder as subcomponents is known (for example, Patent Document 1 (Special No. 2012-43567))). In such an air electrode, a carbon material or the like is used as an electron conductive material. Further, organic binders such as polyvinylidene fluoride, polytetrafluoroethylene and styrene / butadiene rubber are used as the binder.

Recently, a technique for improving the characteristics of the air electrode (hydroxide ion conductivity, electron conductivity and catalytic reaction activity) by using carbon nanotubes as a binder has been proposed. For example, Patent Document 2 (International Publication No. 2016/208769) discloses an air electrode including a plurality of carbon nanotubes (CNT) and a plurality of layered composite hydroxide (LDH) particles supported by the carbon nanotubes. Is disclosed. In this document, CNT is used as a material exhibiting three functions of an inorganic binder, an oxygen reduction generation catalyst, and an electron conductor, while LDH particles are used as a material exhibiting hydroxide ion conductivity.

On the other hand, a layered double hydroxide (LDH) separator having hydroxide ion (OH ⁻ ) conductivity has been proposed in the field of zinc-air secondary batteries. For example, in Patent Document 3 (International Publication No. 2013/073292), in a zinc-air secondary battery, both short-circuit between positive and negative electrodes due to zinc dendrite during charging and mixing of carbon dioxide into the electrolyte are prevented. Therefore, it is disclosed that the air electrode and the negative electrode are separated from each other by an LDH separator. Patent Document 4 (International Publication No. 2016/076047) discloses a separator structure including an LDH separator combined with a porous substrate, and the LDH separator is gas-impermeable and / or It is disclosed to have high density enough to have water impermeability. Further, the LDH separator is composed of an aggregate of a plurality of LDH plate-like particles, and the plurality of LDH plate-like particles are oriented so that their plate surfaces intersect the surface of the porous substrate perpendicularly or obliquely. It is also disclosed that it is oriented.

JP 2012-43567 A International Publication No. 2016/208769 International Publication No. 2013/073292 International Publication No. 2016/076047

Patent Document 2 also proposes providing an LDH separator between the air electrode and the negative electrode in order to prevent a short circuit due to zinc dendrite. However, actually, in order to join the air electrode layer containing CNT and LDH particles to the LDH separator with sufficient strength, it is necessary to use a polymer adhesive. Otherwise, it was difficult to bond the air electrode layer to the LDH separator with sufficient strength. For this reason, if the air electrode layer and the LDH separator can be directly bonded without interposing an adhesive between the air electrode layer and the LDH separator, it can be said that it is more desirable from the viewpoint of reducing the resistance at the bonding interface. .

The present inventors have recently converted LDH powder into metal oxide powder, applied a paste or slurry containing the obtained metal oxide powder and CNT to an LDH separator, and subjected to steam treatment to convert the metal oxide into LDH. It was found that the air electrode layer and the LDH separator can be directly joined while ensuring the desired adhesive strength by returning to the above.

Therefore, an object of the present invention is to directly bond an air electrode layer containing LDH and CNT to an LDH separator while ensuring a desired adhesive strength.

According to one aspect of the invention, providing a layered double hydroxide (LDH) powder;
Firing the LDH powder at 400 to 850 ° C. for 1 to 10 hours to obtain a metal oxide powder;
Mixing the metal oxide powder, carbon nanotubes and solvent to form a paste or slurry;
Applying the paste or slurry to the surface of the LDH separator;
Subjecting the LDH separator coated with the paste or slurry to steam treatment to convert the metal oxide into LDH, thereby obtaining an air electrode layer on the LDH separator;
A method for producing a separator / air electrode composite is provided.

It is a schematic cross section of a separator / air electrode composite. FIG. 3 is a diagram schematically showing the inside of an autoclave used in hydrothermal treatment in Example 1. 3 is a diagram showing an XRD profile obtained by X-ray diffraction in Example 1. FIG. The SEM secondary electron image observed by ion milling the cross section of the air electrode layer obtained in Example 1 is shown. The SEM secondary electron image which observed the fracture surface of the air electrode layer obtained in Example 1 as it is is shown.

TECHNICAL FIELD The present invention relates to a method for manufacturing a separator / air electrode composite. In the method of the present invention, (a) an LDH powder is prepared, (b) the LDH powder is fired to obtain a metal oxide powder, (c) the metal oxide powder, the carbon nanotube and the solvent are mixed, and (d) obtained. (E) Applying the applied LDH separator to steam treatment to convert the metal oxide into LDH, thereby obtaining an air electrode layer on the LDH separator. including. Thus, by converting the LDH powder into a metal oxide powder, the paste or slurry containing the obtained metal oxide powder and CNT is applied to an LDH separator, and steam treatment is performed to return the metal oxide to LDH. The air electrode layer and the LDH separator can be directly joined while ensuring a desired adhesive strength. As described above, an air electrode containing LDH and CNT is already known (see, for example, Patent Document 2), but an LDH separator has an air electrode layer containing CNT and LDH particles (air electrode layer) having sufficient strength for the LDH separator. It was necessary to use a polymer adhesive in order to join them with each other. Otherwise, it was difficult to bond the air electrode layer to the LDH separator with sufficient strength. For this reason, if the air electrode layer and the LDH separator can be directly bonded without interposing an adhesive between the air electrode layer and the LDH separator, it can be said that it is more desirable from the viewpoint of reducing the resistance at the bonding interface. . In this regard, according to the method of the present invention, the above-mentioned problems can be solved and direct bonding between the CNT and LDH-containing air electrode layer and the LDH separator can be realized.

(A) Preparation of LDH powder First, a layered double hydroxide (LDH) powder is prepared. Commercially available LDH powder can be used. A typical LDH powder has the general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · mH ₂ O (where M ²⁺ is a divalent cation and M ³⁺ is a trivalent). 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. 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- can be any anion, but preferred examples include OH ^- and CO ₃ ^2- . Accordingly, the general formula is at least ^{M 2+} is ^{Mg 2+,} include ^{M 3+} is ^{Al 3+, A n-is} 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 average particle diameter D50 of the LDH powder is preferably from 0.1 to 50 μm, more preferably from 0.1 to 10 μm, still more preferably from 0.1 to 5 μm. When the average particle diameter D50 is such, it becomes easy to form an air electrode layer having a desired porosity, and the air electrode characteristics are easily improved.

(B) Firing step The LDH powder is fired under predetermined conditions to obtain a metal oxide powder. That is, LDH, which is a metal-containing hydroxide, is converted into a metal oxide by firing. A preferred firing temperature is 400 to 850 ° C., more preferably 700 to 800 ° C. The preferred firing time at the above firing temperature is 1 to 10 hours, more preferably 3 to 10 hours. The firing of the LDH powder is preferably performed in an oxidizing atmosphere from the viewpoint of promoting the addition to the metal oxide. Examples of the oxidizing atmosphere include air and oxygen. However, the firing atmosphere is not particularly limited as long as the metal oxide powder is obtained, and may be a non-oxidizing atmosphere such as nitrogen.

(C) Mixing Step The metal oxide powder (that is, LDH-derived metal oxide) obtained in the above (b), the carbon nanotube (CNT), and the solvent are mixed to form a paste or slurry. The mixture may be a paste or a slurry as long as it can be applied without problems in the subsequent application process. A paste is preferred because it is easier to apply. The paste or slurry is preferably adjusted to a viscosity of 0.1 to 200 Pa · s before application. The viscosity can be adjusted by mixing the paste or slurry while heating to volatilize the solvent.

CNT is a fibrous carbon material in which graphene having a hexagonal lattice structure is formed in a cylindrical shape. The CNT may be a single-wall (single wall) carbon nanotube or a multi-wall (multi-wall) carbon nanotube. Both ends of the CNT may be closed or open. It is known that CNT mainly exhibits the following three functions in the air electrode layer (see, for example, Patent Document 2).
-CNT functions as an inorganic binder. That is, CNT can contribute to maintaining the shape of the air electrode layer by binding LDH.
-CNT also functions as an air electrode catalyst (oxygen reduction generation catalyst). That is, by including CNT in the air electrode layer, the catalytic reaction activity of the air electrode layer can be improved.
-CNT also functions as an electron conductor. That is, by containing CNT in the air electrode layer, the electron conductivity of the air electrode layer can be improved.

It is preferable that the CNTs exist in the air electrode layer in a bundled state rather than in a bundle shape. Thereby, LDH can be bound efficiently. Therefore, when forming the paste or slurry, it is preferable that the mixing be performed carefully so that the CNTs are unbundled. For example, mortar mixing is preferred. However, some of the CNTs may exist in a bundle in the air electrode layer.

The mixing ratio of the metal oxide powder and CNT is not particularly limited. The amount of CNT added is preferably such that the volume ratio (CNT volume / (CNT volume + metal oxide powder volume) to the total volume of the metal oxide powder and CNT is 0.001 to 0.9, more preferably 0.01 to 0.5.

The solvent used for mixing is not particularly limited as long as it does not deteriorate the properties of CNT and LDH. For example, alcohol such as ethanol or water may be used.

If desired, an air electrode catalyst other than CNTs may be added to the slurry or paste. Preferred examples of such an air electrode catalyst other than CNT include carbon-based materials having a redox catalyst function such as graphite, metals having a redox catalyst function such as platinum and nickel, perovskite oxides, manganese dioxide, oxidation Examples thereof include inorganic oxides having a redox catalyst function such as nickel, cobalt oxide, and spinel oxide. The shape of such an air electrode catalyst is not particularly limited, but is preferably a particle shape.

If desired, a binder other than CNT may be added to the slurry or paste. The binder may be a thermoplastic resin or a thermosetting resin and is not particularly limited. Preferred examples include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, and tetrafluoro. Ethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, fluorine Vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene Pyrene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether -Tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, carboxymethylcellulose (CMC), methylcellulose (MC), cellulose acetate phthalate (CAP), hydroxypropylmethylcellulose (HPMC), hydroxypropylmethylcellulose phthalate (HPMCP) ), Polyvinyl alcohol (PVA) and any mixtures thereof.

(D) Coating step The paste or slurry obtained in the above step (c) is coated on the surface of the LDH separator. The LDH separator is a known ceramic separator containing layered double hydroxide (LDH), and a preferred embodiment thereof will be described later. As shown in FIG. 1, in the case of the LDH separator 12 combined with the porous substrate 14, the paste or slurry is applied to the exposed surface of the LDH separator 12 (the surface opposite to the porous substrate 14). Application of the paste or slurry may be performed by a known method, but is preferably performed by a method that finally brings porosity to the air electrode layer. Preferable examples of the application method include application and printing using an application tool (iron, spatula, brush, spray, dispenser, mono pump, etc.). In any case, an appropriate application method may be appropriately selected according to the viscosity of the paste or slurry to be used.

(E) Steam treatment step The LDH separator coated with paste or slurry is subjected to steam treatment to convert the metal oxide into LDH, thereby forming the air electrode layer 16 on the LDH separator 12 as shown in FIG. obtain. The steam treatment is performed by exposing the LDH separator to steam or moisture. Therefore, the steam treatment can be rephrased as a humidification treatment. The steam treatment is preferably performed at 0 to 200 ° C., more preferably 50 to 180 ° C., and still more preferably 100 to 150 ° C. The steam treatment is preferably performed in an autoclave (sealed container). In particular, steam treatment performed at a high temperature (for example, 100 ° C. or higher) in an autoclave is generally referred to as hydrothermal treatment or hydrothermal synthesis, and can be said to be particularly preferable from the viewpoint of production efficiency and the like. However, since it is possible to convert the metal oxide to LDH simply by humidification, steam treatment at a low temperature of at least 0 ° C. can also be employed.

The time of the steam treatment at the above-mentioned temperature is preferably 0.1 hour or more, more preferably 0.5 to 20 hours, and further preferably 1 to 10 hours. With such a time, it is possible to avoid or reduce the occurrence of a heterogeneous phase by sufficiently reproducing the LDH. The steam treatment time is not particularly problematic if it is too long, but it may be set in a timely manner with emphasis on efficiency.

The steam treatment is preferably performed in the presence of ion-exchanged water, and more preferably performed in an autoclave containing ion-exchanged water. Conversion of metal oxide to LDH (regeneration of LDH) requires the incorporation of the above-described n-valent anion (A ⁿ⁻ ) as an LDH component, but in the air when ion-exchanged water is used, LDH is regenerated by incorporating carbonate ions (CO ₃ ²⁻ ) derived from carbon dioxide. Of course, instead of the ion-exchanged water, the steam treatment may be performed in the presence of the above-described aqueous solution containing the n-valent anion (A ⁿ⁻ ).

The air electrode layer obtained as described above is typically porous. By being porous, the surface area in contact with air can be increased, and the performance of the air electrode can be improved.

The separator / air electrode composite produced by the method of the present invention can be preferably used as a combination of an air electrode (also referred to as an oxygen electrode) and a separator in various electrochemical devices. Preferable examples of such electrochemical devices include metal-air batteries such as zinc-air batteries, alkaline fuel cells, salt electrolyzers, water electrolyzers and the like.

LDH separator LDH separator 12 is a ceramic separator containing layered double hydroxide (LDH). As described above, the LDH separator 12 is known as a dense separator having hydroxide ion conductivity in the field of zinc secondary batteries. A preferred LDH separator 12 is gas impermeable and / or water impermeable. In other words, the LDH separator 12 is preferably so dense that it has gas impermeability and / or water impermeability. In this specification, “having gas impermeability” means that an object to be measured (that is, LDH separator 12 and / or porous material) in water as described in Patent Document 4 (International Publication No. 2016/076047). This means that even if helium gas is brought into contact with one surface side of the porous substrate 14) with a differential pressure of 0.5 atm, no bubbles are generated due to helium gas from the other surface side. Further, in this specification, “having water impermeability” means that, as described in Patent Document 4, water in contact with one surface side of an object to be measured (for example, an LDH film and / or a porous substrate) is used. It means that it does not transmit to the other side. That is, the fact that the LDH separator 12 has gas impermeability and / or water impermeability means that the LDH separator 12 has a high degree of denseness that does not allow gas or water to pass through. Or it means that it is not a porous film or other porous material having air permeability. By doing so, the LDH separator 12 selectively allows only hydroxide ions to pass due to its hydroxide ion conductivity. Accordingly, since the LDH separator 12 is interposed between the air electrode and the negative electrode in the metal-air secondary battery, it is possible to prevent the carbon dioxide from being mixed into the electrolytic solution. It is possible to prevent the deterioration of the battery and avoid the deterioration of the battery performance. Moreover, due to the denseness and hardness, it is possible to prevent a short circuit between the positive and negative electrodes due to zinc dendrite during charging of the zinc-air secondary battery. As a result, it is possible to configure a highly reliable metal-air battery (particularly a metal-air secondary battery) that is less susceptible to characteristic deterioration. Needless to say, the LDH separator 12 may be combined with the porous substrate 14 as shown in FIG.

The LDH separator 12 includes a layered double hydroxide (LDH), and is preferably composed of LDH. As is generally known, LDH is composed of a plurality of hydroxide base layers and an intermediate layer interposed between the plurality of hydroxide base layers. The hydroxide base layer is mainly composed of metal elements (typically metal ions) and OH groups. The intermediate layer of LDH is composed of anions and H ₂ O. The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anion in LDH comprises OH ^- and / or CO ₃ ^2- . LDH has excellent ionic conductivity due to its inherent properties.

In general, LDH is M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · mH ₂ O (where M ²⁺ is a divalent cation and 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). It is known as a representative. In the above basic composition 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- can be any anion, but preferred examples include OH ^- and CO ₃ ^2- . Accordingly, in the above basic ^{formula, M 2+} comprises ^{Mg 2+, M 3+} comprises ^{Al 3+, A n-is} 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 an arbitrary number which means the number of moles of water, and is a real number of 0 or more, typically more than 0 or 1 or more. However, the above basic composition formula is merely a formula of “basic composition” that is typically exemplified with respect to LDH in general, and the constituent ions can be appropriately replaced. For example, it may be replaced with some or all of the M ³⁺ tetravalent or higher valency cations in the basic formula, in which case, the anion A coefficient of ^n-x / n in the general formula May be changed as appropriate.

For example, the hydroxide base layer of LDH may be composed of Ni, Ti, OH groups and possibly inevitable impurities. As described above, the intermediate layer of LDH is composed of an anion and H ₂ O. The alternate layered structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the commonly known alternate layered structure of LDH, but the LDH of this embodiment is mainly composed of Ni, By comprising Ti and OH groups, excellent alkali resistance can be exhibited. Although the reason is not necessarily clear, it is considered that an element (for example, Al) that is considered to be easily eluted in an alkaline solution is not intentionally or actively added to the LDH of this embodiment. Nevertheless, the LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH can take the form of nickel ions. The nickel ions in LDH are typically considered to be Ni ²⁺ , but are not particularly limited because other valences such as Ni ³⁺ may also exist. Ti in LDH can take the form of titanium ions. The titanium ion in LDH is typically considered to be Ti ⁴⁺ , but is not particularly limited because other valences such as Ti ³⁺ may also exist. Inevitable impurities are optional elements that can be inevitably mixed in the manufacturing process, and can be mixed in LDH, for example, derived from raw materials and base materials. As described above, since the valences of Ni and Ti are not necessarily certain, it is impractical or impossible to specify LDH strictly by a general formula. If it is assumed that the hydroxide base layer is mainly composed of Ni ²⁺ , Ti ⁴⁺ and OH groups, the corresponding LDH has the general formula: Ni ²⁺ _1-x Ti ⁴⁺ _x (OH) ₂ ^{An _{- 2x / n · mH 2 O}} ( ^{wherein, a n-n-valent} anion, n is an integer of 1 or more, preferably 1 or 2, 0 <x <1, preferably 0.01 ≦ x ≦ 0.5, m is 0 or more, typically greater than 0 or 1 or more real number). However, the above general formula should be construed as “basic composition” only, and other elements or ions (other valences of the same element) to the extent that elements such as Ni ²⁺ and Ti ⁴⁺ do not impair the basic characteristics of LDH. It should be understood that it can be replaced by a number of elements or ions, or elements or ions that may be inevitably mixed in the manufacturing process.

Alternatively, the hydroxide basic layer of LDH may contain Ni, Al, Ti and OH groups. As described above, the intermediate layer is composed of an anion and H ₂ O. The alternate layered structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the generally known alternate layered structure of LDH, but the LDH of this embodiment uses the basic hydroxide layer of LDH as Ni, Al. By comprising a predetermined element or ion containing Ti and OH groups, excellent alkali resistance can be exhibited. The reason for this is not necessarily clear, but the LDH of this embodiment is thought to be because Al, which was previously thought to be easily eluted in an alkaline solution, is less likely to be eluted in an alkaline solution due to some interaction with Ni and Ti. It is done. Nevertheless, the LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH can take the form of nickel ions. The nickel ions in LDH are typically considered to be Ni ²⁺ , but are not particularly limited because other valences such as Ni ³⁺ may also exist. Al in LDH can take the form of aluminum ions. Aluminum ions in LDH are typically considered to be Al ³⁺ , but are not particularly limited because other valences are possible. Ti in LDH can take the form of titanium ions. The titanium ion in LDH is typically considered to be Ti ⁴⁺ , but is not particularly limited because other valences such as Ti ³⁺ may also exist. The hydroxide base layer may contain other elements or ions as long as it contains Ni, Al, Ti and OH groups. However, it is preferable that the hydroxide base layer contains Ni, Al, Ti, and OH groups as main components. That is, the hydroxide base layer is preferably mainly composed of Ni, Al, Ti and OH groups. Therefore, the hydroxide base layer is typically composed of Ni, Al, Ti, OH groups and possibly inevitable impurities. Inevitable impurities are optional elements that can be inevitably mixed in the manufacturing process, and can be mixed in LDH, for example, derived from raw materials and base materials. As described above, since the valences of Ni, Al, and Ti are not necessarily certain, it is impractical or impossible to specify LDH strictly by a general formula. If it is assumed that the hydroxide base layer is mainly composed of Ni ²⁺ , Al ³⁺ , Ti ⁴⁺ and OH groups, the corresponding LDH has the general formula: Ni ²⁺ _1-xy Al ³⁺ _x Ti ⁴⁺ _y (OH) ₂ A ⁿ⁻ _{(x + 2y) / n} · mH ₂ O (where A ⁿ⁻ is an n-valent anion, n is an integer of 1 or more, preferably 1 or 2, and 0 <x <1, preferably 0.01 ≦ x ≦ 0.5, 0 <y <1, preferably 0.01 ≦ y ≦ 0.5, 0 <x + y <1, m is 0 or more, typically 0. It can be represented by a basic composition that exceeds or is one or more real numbers. However, the above general formula should be construed as “basic composition” only, and other elements or ions (of the same element) such that Ni ²⁺ , Al ³⁺ , Ti ^{4+ and the} like do not impair the basic characteristics of LDH. It should be understood that it can be replaced by other valence elements or ions or elements or ions that may be inevitably mixed in the manufacturing process.

The LDH separator 12 may be in the form of a plate, a film, or a layer. When the LDH separator 12 is in the form of a film or a layer, the film or layer LDH separator 12 is combined with the porous substrate 14. For example, it is preferably formed on or in the porous substrate 14. A preferable thickness of the plate-like LDH separator 12 is 0.01 to 0.5 mm, more preferably 0.02 to 0.2 mm, and still more preferably 0.05 to 0.1 mm. The hydroxide ion conductivity of the LDH separator 12 is preferably as high as possible, but typically has a conductivity of 10 ⁻⁴ to 10 ⁻¹ S / m. On the other hand, in the case of a film-like or layered form, the thickness 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. Thus, the resistance of the LDH separator 12 can be reduced by being thin. The lower limit of the thickness is not particularly limited because it varies depending on the application, but in order to ensure a certain degree of rigidity desired as a separator film or layer, the thickness is preferably 1 μm or more, more preferably 2 μm or more. is there.

The LDH separator 12 is preferably combined with the porous substrate 14. In particular, the porous substrate 14 is preferably provided on one side of the LDH separator 12. When the porous substrate 14 is provided on one side of the LDH separator 12, the porous substrate 14 is provided on the surface of the LDH separator 12 opposite to the air electrode layer 16 (surface on the negative side in the metal-air battery). . The porous substrate 14 has water permeability, so that the electrolytic solution can reach the LDH separator 12. In addition, since the strength can be imparted by the porous base material 14, the LDH separator 12 can be thinned to reduce the resistance. In addition, a dense film or dense layer of LDH can be formed on or in the porous substrate 14. In the case where a porous substrate is provided on one side of the LDH separator 12, a method of preparing a porous substrate and depositing LDH on the porous substrate is conceivable.

The porous substrate 14 is preferably composed of at least one selected from the group consisting of a ceramic material, a metal material, and a polymer material, more preferably a ceramic material and / or a polymer material, still more preferably. It is a polymer material. 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, and any combination thereof, and more preferable. Is alumina, zirconia, titania, and any combination thereof, particularly preferably alumina and zirconia, most preferably alumina. When these porous ceramics are used, it is easy to form the LDH separator 12 having excellent denseness. Preferable examples of the metal material include aluminum and zinc. Preferable examples of the polymer material include polystyrene, polyether sulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrofluorinated fluororesin (tetrafluorinated resin: PTFE, etc.), and any combination thereof. It is further preferable to appropriately select a material excellent in alkali resistance as the resistance to the electrolytic solution from the various preferable materials described above.

Preferably, the LDH separator 12 is composed of an aggregate of a plurality of LDH plate-like particles, and the plurality of LDH plate-like particles have their plate surfaces on the surface of the porous substrate 14 (ignoring fine irregularities caused by the porous structure). The orientation is such that it intersects perpendicularly or diagonally with the main surface of the porous substrate when observed macroscopically as much as possible. The LDH separator 12 may be at least partially incorporated in the pores of the porous base material 14, and in that case, LDH plate-like particles may also exist in the pores of the porous base material 14.

The manufacturing method of the LDH separator 12, for example, the LDH separator 12 combined with the porous substrate 14 is not particularly limited, and the LDH separator 12 is manufactured by referring to a known manufacturing method (for example, Patent Documents 3 and 4). be able to.

The present invention will be described more specifically with reference to the following examples.

Example 1
(1) Production of Separator / Air Electrode Composite Commercially available Mg—Al LDH powder (DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd., composition: Mg ²⁺ _0.75 Al ³⁺ _0.25 (OH) ₂ CO ₃ ^{n _{- 0.25 / n · mH 2 O}} ) was prepared. This LDH powder was calcined at 650 ° C. for 5 hours in the air atmosphere to be converted into a metal oxide powder. On the other hand, single-walled CNT (product name: SWNT dispersion, manufactured by Meijo Nano Carbon Co., Ltd.) was dispersed in ethanol to obtain a CNT dispersion. The metal oxide powder and the CNT dispersion were weighed so that the volume ratio of (CNT) :( metal oxide) was 5:95, and placed in a mortar and mixed thoroughly. At this time, by mixing while heating the mortar with a hot stirrer, ethanol was volatilized to adjust the viscosity of the mixture. As shown in FIG. 1, the paste thus obtained was applied with a trowel onto the surface of an LDH separator combined with porous alumina. This porous alumina / LDH separator composite material was prepared according to Example 2 described later. The LDH separator coated with the paste was placed in an autoclave and hydrothermally treated at 100 ° C. for 5 hours. At this time, as shown in FIG. 2, ion-exchanged water 102 is contained in the autoclave 100, and an LDH separator 106 coated with a paste is placed on a Teflon (registered trademark) dish 104 floated on the ion-exchanged water 102. Was placed. Thus, the metal oxide was converted to LDH (that is, LDH was regenerated) to obtain a separator / air electrode composite.

(2) Evaluation of separator / air electrode composite The following evaluation was performed on the separator / air electrode composite.

(2a) X-ray diffraction When X-ray diffraction was performed on the air electrode layer of the separator / air electrode composite, the XRD profile shown in FIG. 3 was obtained. FIG. 3 also shows the XRD profile of the composite before hydrothermal treatment and the XRD profile of the LDH separator without the air electrode layer. As is clear from the results shown in FIG. 3, the metal oxide was converted to LDH by hydrothermal treatment, that is, the air electrode layer containing CNT and LDH powder was formed in a form that was directly bonded onto the LDH separator. I understand. Although the XRD profile of LDH separator without the air electrode layer seen the peak derived from Al ₂ O _3, which is understood to be due to the porous alumina complexed with LDH separator.

(2b) Evaluation of adhesive strength The strength of the air electrode layer bonded to the LDH separator was evaluated by a peel test. In the peel test, only the air electrode part was lifted, and it was confirmed that the separator peeled off due to its own weight and did not fall. As a result, it was confirmed that the air electrode layer was bonded to the LDH separator with sufficient strength. In addition to the above peel test, the tensile strength may be evaluated using an autograph manufactured by Shimadzu Corporation.

(2c) Microstructure observation The surface microstructure and the cross-sectional microstructure of the air electrode layer were observed at an acceleration voltage of 20 kV using a scanning electron microscope (SEM) (JSM-6610LV, manufactured by JEOL Ltd.). Was sufficiently porous. FIG. 4 shows a secondary electron image observed by ion milling the cross section of the air electrode layer, and FIG. 5 shows a secondary electron image obtained by observing the broken surface of the air electrode layer as it is. FIG. 4 clearly confirms that the air electrode layer is porous including LDH plate-like particles, while FIG. 5 clearly confirms the presence of CNT as the fibrous material.

Example 2 (Reference)
A functional layer and a composite material containing Mg and Al-containing LDH were prepared and evaluated by the following procedure. The functional layer in this example corresponds to an LDH separator.

(1) Preparation of porous substrate 70 parts by weight of a dispersion medium (xylene: butanol = 1: 1) and binder (polyvinyl butyral: Sekisui Chemical) with respect to 100 parts by weight of alumina powder (AES-12, manufactured by Sumitomo Chemical Co., Ltd.) BM-2 manufactured by Kogyo Co., Ltd. 11.1 parts by weight, 5.5 parts by weight of a plasticizer (DOP: manufactured by Kurokin Kasei Co., Ltd.), and 2.9 parts by weight of a dispersant (Rheodor SP-O30 manufactured by Kao Corporation) The mixture was stirred and degassed by stirring under reduced pressure to obtain a slurry. The slurry was molded into a sheet shape on a PET film using a tape molding machine so that the film thickness after drying was 220 μm to obtain a sheet molded body. The obtained molded body was cut out to have a size of 2.0 cm × 2.0 cm × thickness 0.022 cm and fired at 1300 ° C. for 2 hours to obtain an alumina porous substrate.

For the obtained porous substrate, the porosity of the porous substrate was measured by the Archimedes method and found to be 40%.

Further, when the average pore diameter of the porous substrate was measured, it was 0.3 μm. 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) Polystyrene spin coating and sulfonation 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 an alumina 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.

(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 70 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 an aqueous raw material solution.

(4) 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 (3) above and the porous substrate sulfonated in (2) above Was enclosed 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. Thereafter, a hydrothermal treatment was performed at a hydrothermal temperature of 70 ° C. for 168 hours (7 days) to form an LDH alignment film on the substrate surface. After a lapse of a predetermined time, the substrate was taken out from the sealed container, washed with ion-exchanged water, dried at 70 ° C. for 10 hours, and a part of the functional layer containing LDH was incorporated into the porous substrate. Got in shape. The thickness of the functional layer obtained was about 3 μm (including the thickness of the portion incorporated in the porous substrate).

(5) Evaluation result The following evaluation was performed with respect to the obtained functional layer or composite material.

(5a) Identification of functional layer Using an X-ray diffractometer (RINT TTR III manufactured by Rigaku Corporation), the crystal phase of the functional layer is measured under the measurement conditions of voltage: 50 kV, current value: 300 mA, measurement range: 10 to 70 °. As a result, an XRD profile was obtained. About the obtained XRD profile, JCPDS card NO. Identification was performed using a diffraction peak of LDH (hydrotalcite compound) described in 35-0964. As a result, it was identified from the obtained XRD profile that the functional layer was LDH (hydrotalcite compound).

(5b) Observation of microstructure The surface microstructure of the functional layer was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV. Further, after obtaining a cross-sectional polished surface of a functional layer (a film-shaped portion made of an LDH film and a composite portion made of LDH and a base material) with an ion milling device (manufactured by Hitachi High-Technologies Corporation, IM4000) The structure was observed by SEM under the same conditions as the observation of the surface microstructure, and as a result, the functional layer was composed of a film-shaped portion composed of an LDH film and a composite composed of LDH and a porous substrate located under the film-shaped portion. In addition, the LDH constituting the film-like part is composed of an aggregate of a plurality of plate-like particles, and the plate-like surfaces of the plurality of plate-like particles are porous bases. Oriented perpendicularly or diagonally to the surface of the material (the surface of the porous substrate when macroscopic observations resulting from the porous structure are negligibly macroscopic). In the pores of the porous substrate LDH has constituted the dense layer is filled.

(5c) Gas impermeability and water impermeability For the functional layer, based on the technique described in Patent Document 4 (International Publication No. 2016/076047), helium gas is reduced to 0 on one side of the composite material in water. When contact was made at a differential pressure of .5 atm, generation of bubbles due to helium gas was not observed from the other side. Moreover, based on the method described in patent document 4, it confirmed that the water which contacted the one surface side of the composite material did not permeate | transmit the other surface side. That is, it was confirmed that the functional layer or the composite material has gas impermeability and / or water impermeability.

Claims (9)

1. Preparing a layered double hydroxide (LDH) powder;
   Firing the LDH powder at 400 to 850 ° C. for 1 to 10 hours to obtain a metal oxide powder;
   Mixing the metal oxide powder, carbon nanotubes (CNT) and a solvent to form a paste or slurry;
   Applying the paste or slurry to the surface of the LDH separator;
   Subjecting the LDH separator coated with the paste or slurry to steam treatment to convert the metal oxide into LDH, thereby obtaining an air electrode layer on the LDH separator;
   A method for producing a separator / air electrode composite, comprising:
2. The method according to claim 1, wherein the firing of the LDH powder is performed in an oxidizing atmosphere.
3. The method according to claim 1 or 2, wherein the steam treatment is performed at 0 to 200 ° C.
4. The method according to any one of claims 1 to 3, wherein the steam treatment is performed in an autoclave.
5. The method according to any one of claims 1 to 4, wherein an average particle diameter D50 of the LDH powder is 0.1 to 50 µm.
6. The method according to any one of claims 1 to 5, wherein the air electrode layer is porous.
7. The method according to any one of claims 1 to 6, wherein the LDH separator has gas impermeability and / or water impermeability.
8. The method according to any one of claims 1 to 7, wherein the LDH separator is combined with a porous substrate.
9. The LDH separator is composed of an aggregate of a plurality of LDH plate-like particles, and the plurality of LDH plate-like particles are oriented so that their plate surfaces intersect perpendicularly or obliquely with the surface of the porous substrate. The method of claim 8, wherein the method is oriented.
   
   
   
   

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